6-acyloryalkyl-1,4-dihydropyridine derivatives and a method of effecting vasodilation therewith

ABSTRACT

This invention relates to 1,4-dihydropyridine derivatives. More particularly, it relates to new 1,4-dihydropyridine derivatives thereof which have vasodilating and anti-hypertensive activity, to processes for the preparation thereof, and to pharmaceutical composition comprising the same for therapeutical treatment in cardiovascular diseases and hypertension in human being.

BACKGROUND OF THE INVENTION

Accordingly, one object of this invention is to provide new and useful 1,4-dihydropyridine derivatives.

Another object of this invention is to provide processes for the preparation of 1,4-dihydropyridine derivatives.

A further object of this invention is to provide useful pharmaceutical composition comprising said 1,4-dihydropyridine derivatives as a vasodilator and anti-hypertensive.

Still further object of the present invention is to provide a therapeutical method of treating cardiovascular diseases such as coronary insufficiency, angina pectoris or myocardial infarction and hypertension.

The 1,4-dihydropyridine derivatives of this invention may be represented by the general formula: ##STR1## wherein R₁ is aryl which may have one or more suitable substituent(s) or a heterocyclic group,

R₂ and R₃ are each, same or different, esterified carboxy, and

R₄ and R₅ are each hydrogen, cyano; lower alkyl; or substituted lower alkyl in which the substituent is cyano, hydroxy, acyloxy, hydroxyimino, hydrazono, lower alkoxyimino, hydroxy(lower)alkylimino, N'- or N', N'-di-(lower)alkylamino(lower)alkylimino, hydrazino, hydroxy(lower)alkylamino, N'- or N', N'-di-(lower)alkylamino(lower)alkylamino, a 5 or 6-membered saturated N-containing heterocyclic-1-yl which may have hydroxy, lower alkyl or hydroxy(lower)alkyl, or oxo wherein thus formed carbonyl may be protected with suitable protecting group; provided that, when one of R₄ and R₅ is hydrogen or lower alkyl, the other is always cyano or said substituted lower alkyl, and when R₄ and R₅ are not hydrogen or lower alkyl, both of them are a group selected from cyano and said substituted lower alkyl,

Or R₄ is hydrogen or lower alkyl and R₃ and R₅ are combined to form a group of the formula: ##STR2## wherein R₆ is hydrogen or methyl and R₇ is 2-(N,N-diethylamino)-ethyl or 2-hydroxyethyl.

The terms used in the definitions of the symbols of the general formulae given in this specification and claims are explained as follows:

The term "lower" used in connection with an alkylene, alkyl and alkenyl is intended to mean the one having 1 to 8 carbon atoms.

Aryl and aryl moiety may be phenyl, naphthyl, xylyl, tolyl, mesityl, cumenyl and the like, which may have one or more suitable substituent(s). Preferred examples of the suitable substituent(s) are halogen, nitro, hydroxy, halo(lower)alkyl, lower alkoxy and lower alkenyloxy. Halogen or halo moiety is fluorine, chlorine, bromine or iodine.

Lower alkylene may be one having a straight or branched and saturated bivalent hydrocarbon chain such as methylene, ethylene, methylmethylene, trimethylene, propylene or tetramethylene.

Lower alkyl and lower alkyl moiety may be ones having a straight or branched and saturated hydrocarbon chain such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl, neo-pentyl, hexyl, heptyl or octyl,

Lower alkoxy and lower alkoxy moiety may be methoxy, ethoxy, proposy, isopropoxy, butoxy, t-butoxy and pentyloxy.

Halo(lower)alkyl may be mono-halo(lower)alkyl such as chloromethyl, bromomethyl or chloropropyl; di-halo(lower)alkyl such as 1,2-dichloroethyl, 1,2-dibromoethyl or 2,2-dichloroethyl; and tri-halo(lower)alkyl such as trifluoromethyl or 1,2,2-trichloroethyl.

Lower alkenyl and lower alkenyl moiety may be ones having a straight or branched hydrocarbon chain which contains one or more double bond(s), such as vinyl, allyl, butenyl, butanedienyl or penta-2,4-dienyl.

Acyl and acyl moiety may be lower alkanoyl such as formyl, acetyl, propionyl, butyryl, isobutyryl, valeryl, isovaleryl, pivaloyl; substituted lower alkanoyl, for example, carboxy(lower)alkanoyl, esterified carboxy(lower)alkanoyl such as lower alkoxycarbonyl(lower)alkanoyl, N- or N,N-di-substituted amino(lower)alkanoyl such as N- or N,N-di-(lower)alkylamino(lower)alkanoyl (e.g. N-methyl (or N,N-dimethyl) aminoacetyl, 1(or 2)- N-ethyl(or N,N-diethyl)amino!propionyl or 1(or 2)- N-methyl-N-ethylamino!propionyl) or N-lower alkyl -N-ar(lower)alkylamino(lower)alkanoyl (e.g. 1-(or 2)- N-methyl-N-benzylamino!propionyl) or aryloxy(lower)alkanoyl such as phenoxyacetyl, tolyloxyacetyl, 2(or 3 or 4)-chlorophenoxyacetyl, 2- 2(or 3 or 4)-chlorophenoxy!-propionyl, (2(or 3 or 4)-nitrophenoxyacetyl or 2(or 3 or 4)-methoxyphenoxyacetyl); aroyl such as benzoyl, naphthoyl or toluoyl and the like.

A heterocyclic group for R₁ may be an aromatic heterocyclic group containing one or more hetero atom(s) selected form nitrogen atom, sulfur atom and oxygen atom, for example, thienyl, furyl, pyrrolyl, thiazolyl, thiadiazolyl, tetrazolyl, pyridyl, pyrimidinyl, quinolyl, isoquinolyl, benzothienyl, indolyl or purinyl.

Esterified carboxy for R₂ and R₃ may be lower alkoxycarbonyl such as methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, t-butoxycarbonyl; halo(lower)alkoxycarbonyl such as the halo-analogues of the above-mentioned lower alkoxycarbonyl (e.g., 2-bromoethoxycarbonyl, 2-chloroethoxycarbonyl, 2(or 3)-chloropropoxycarbonyl, 2(or 3)-bromopropoxycarbonyl, 2,2-dichloroethoxycarbonyl or 2,2,2-trichloroethoxycarbonyl); hydroxy(lower)alkoxycarbonyl such as 2-hydroxyethoxycarbonyl or 2(or 3)-hydroxypropoxycarbonyl; lower alkoxy(lower)alkoxycarbonyl such as 2-methoxyethoxycarbonyl, 2-ethoxyethoxycarbonyl or 2(or 3)-methoxy(or ethoxy)propoxycarbonyl; aryloxycarbonyl such as phenoxycarbonyl, tolyloxycarbonyl, xylyloxycarbonyl or p-chlorophenoxycarbonyl; ar(lower)alkoxycarbonyl such as benzyloxycarbonyl, p-bromobenzyloxycarbonyl, o-methoxybenzyloxycarbonyl or phenethyloxycarbonyl; ar(lower)alkoxy(lower)alkoxycarbonyl such as 2-(benzyloxy)ethoxycarbonyl or 2(or 3)-(benzyloxy)propoxycarbonyl; aryloxy(lower)alkoxycarbonyl such as 2-(phenoxy)ethoxycarbonyl or 2(or 3)-(phenoxy)propoxycarbonyl; N- or N,N-(di)-substituted amino(lower)alkoxycarbonyl such as N- or N,N-(di)-(lower)alkylamino(lower) alkoxycarbonyl (e.g. 1(or 2)- N-methyl (or N,N-dimethyl)aminoethoxycarbonyl, 1(or 2)- N-ethyl(or N,N-diethyl)amino!ethoxycarbonyl, or 1(or 2 )-(N-methyl-N-ethylaminoethoxycarbonyl) or N-lower alkyl-N-ar(lower)alkylamino(lower)alkoxycarbonyl (e.g. 2-(N-methyl-N-benzylamino)-ethoxycarbonyl) and the like, and further R₂ and R₃ may be same or different;

Lower alkyl substituted with oxo includes lower alkanoyl such as formyl, acetyl, propionyl, butyryl, isobutyryl, valeryl, isovaleryl or pivaloyl and lower alkanoyl(lower)alkyl such as formylmethyl, acetonyl, 2-formylethyl, 3-formylpropyl or butyrylmethyl. The carbonyl group thereof may be protected with suitable protecting group, and thus protected carbonyl group in this invention means a group given by protecting the carbonyl with conventionally employed protecting group for a carbonyl. Suitable examples of such protected carbonyl group are acetal, cyclic-acetal thioacetal, cyclic-thioacetal, cyclicmonothioacetal or acylal types of group. Examples of these lower alkyl containing such protected carbonyl group are gem-di(lower)alkoxy(lower)alkyl (e.g. dimethoxymethyl, 1,1-dimethoxyethyl, diethoxymethyl, dipropoxymethyl, 2,2-diethoxyethyl or 2,2-diethoxypropyl); gem-lower alkylenedioxy(lower)alkyl (e.g. 1,3-dioxolan-2-yl, 2-methyl-1,3-dioxolan-2-yl, 4-methyl-1,3-dioxolan-2-yl, 4,5-dimethyl-1,3-dioxolan-2-yl, 1,3-dioxan-2-yl, 2-methyl-1,3-dioxan-2-yl, 1,3-dioxolan-2-ylmethyl, 2-methyl-1,3-dioxolan-2-ylmethyl or 3-(1,3-dioxolan-2-yl)propyl); gem-di(lower)alkylthio(lower)-alkyl (e.g. dimethylthiomethyl, 1,1-dimethylthioethyl, diethylthiomethyl or 2,2-diethylthioethyl); gem-lower alkylenedithio(lower)alkyl (e.g. 1,3-dithiolan-2-yl, 2-methyl-1,3-dithiolan-2 -yl, 4-methyl-1,3-dithiolan-2-yl, 4,5-dimethyl-1,3-dithiolan-2-yl, 1,3-dithian-2-yl, 2-methyl-1,3-dithian-2-yl, 1,3-dithiolan-2-ylmethyl, 2-methyl-1,3-dithiolan-2-ylmethyl or 3-(1,3-dithiolan-2-yl)propyl); and gem-di(lower)alkanoyloxy(lower)alkyl (e.g. diacetoxymethyl, 1,1-diacetoxyethyl, dipropionyloxymethyl or 2,2-dipropionyloxyethyl); 5 or 6-membered saturated 1-oxa-3-thioheterocyclic-1-yl-(lower)alkyl (e.g. 1,3-oxathiolan-2-yl, 2-methyl-1,3-oxathiolan-2-yl, 4-methyl-1,3-oxathiolan-2-yl, 4,5-dimethyl-1,3-oxathiolan-2-yl, 1,3-oxothian-2-yl, 2-methyl-1,3-oxothian-2-yl, 1,3-oxathiolan-2-ylmethyl, 2-methyl-1,3-oxathiolan-2-ylmethyl or 3-(1,3-oxathiolan-2-yl)propyl.

A 5 or 6-membered saturated N-containing heterocyclic-1-yl group may be one which may contain additional one or more hetero atom(s) selected from nitrogen, sulfur and oxygen atoms such as pyrrolidin-1-yl, piperidino, imidazolidin-1-yl, morpholino or thiomorpholino, and it may be optionally substituted with hydroxy, lower alkyl or hydroxy(lower)alkyl such as hydroxymethyl, 2-hydroxyethyl, 2-hydroxypropyl or 3-hydroxypropyl.

The other terms of each lower alkoxyimino, N'- or N', N'-di-(lower)alkylamino(lower)alkylimino, hydroxy(lower)alkylimino, N'- or N',N'-di-(lower)alkylamino(lower)alkylamino and hydroxy(lower)alkylamino will be clearly defined by applying optionally the above given exemplifications of the terms to them.

According to the present invention, 1,4-dihydropyridine derivatives (I) can be produced by various processes, which fall into the following classification:

(I Construction of fundamental structure)

1. Ring formation of 1,4-dihydropyridine nucleus.

(II Transformations of functions)

2. Hydrolysis for removal of protecting group of protected carbonyl group

3. Condensation to form imino-function.

4. Dehydration

5. Reduction of oxo- or imino-function.

6. Acylation of hydroxy-function.

7. Oxidation of alcohol to carbonyl compound.

8. Pyrolytic ring closure.

9. Other transformations.

Each of these processes will be hereinafter illustrated.

1. Ring formation of 1,4-dihydropyridine nucleus.

Some of the compound (I) representable by the following formula: ##STR3## wherein R₁, R₂ and R₃ are each as defined above and R_(4a) and R_(5a) are each hydrogen, lower alkyl or lower alkyl substituted with oxo wherein thus formed carbonyl group is protected with suitable protecting group, provided that at least one of R_(4a) and R_(5a) is lower alkyl substituted with oxo wherein thus formed carbonyl group is protected with suitable protecting group, can be prepared by carrying out one of the reactions of the processes, which comprises

(1) reacting a compound of the formula: ##STR4## wherein R₁, R₃ and R_(5a) are each as defined above, with an amino compound of the formula: ##STR5## wherein R₂ and R_(4a) are each as defined above, (2) subjecting a mixture of an aldehyde compound of the formula:

    R.sub.1 --CHO                                              (II')

wherein R₁ is as defined above, an ester of β-ketonic acid of the formula:

    R.sub.5a -- COCH.sub.2 -- R.sub.3                          (II")

wherein R₃ and R_(5a) are each as defined above, and an amino compound (III) to reaction, or

(3) reacting an acetylene compound of the formula:

    R.sub.2 -- C.tbd.C-- R.sub.4a                              (III')

wherein R₂ and R_(4a) are each as defined above, with ammonia or an ammonium salt and a compound (II).

The starting compound (II) used in the reactions (1) and (3) may be novel and prepared by reacting the aldehyde (II') with the β-ketoacid ester (II") in a conventional manner, and the ammonium salt used in the reaction (3) includes an inorganic ammonium salt such as ammonium chloride or ammonium sulfate, or an organic ammonium salt such as ammonium acetate.

In the above reactions (1), (2) and (3), there can be employed the starting compounds (II), (II"), (III) and (III") wherein the symbols R_(4a) and R_(5a) are occasionally exchanged into each other, even when both symbols are not the same groups, and, in such case, the substantially same object compound (I-1) may be obtained not only when R_(4a) and R_(5a) are the same groups, irrespective of R₂ and R₃ being the same groups or not, but also when R_(4a) and R_(5a) are not the same groups and R₂ and R₃ are the same groups.

Regarding the reactions (1) and (3), the starting compound (II) may include geometric isomers such as cis-trans isomers due to the double bond in its molecule. Such cis-trans isomers may be equilibrated and, therefore, each or a mixture of the isomers of (II) may be applied as the starting materials to provide the same object compound (I-1).

The reactions (1), (2) and (3) can be carried out at ambient temperature or under warming or heating with or without a suitable solvent such as benzene, toluene, xylene, chloroform, carbon tetrachloride, methylene chloride, ethylene chloride, methanol, propanol, butanol, water or other conventional solvents. The reactions can be usually promoted in the presence of an agent such as an acid (e.g. acetic acid), a base (e.g. pyridine or picoline) or in a conventional buffer solution. These agents may act as a reaction promotor and also used as a solvent when they are in liquid. The reactions can be also accelerated by heating. The reaction condition may vary according to the kind of the reactants to be used.

2. Hydrolysis for removal of protecting group of protected carbonyl group. The compound of the formula: ##STR6## wherein R₁, R₂ and R₃ are each as defined above and R_(4b) and R_(5b) are each hydrogen, lower alkyl or lower alkyl substituted with oxo, provided that at least one of R_(4b) and R_(5b) is lower alkyl substituted with oxo, can be prepared by hydrolyzing the compound (I-1) which can be obtained in the above-mentioned ring formation process. In this process, the protecting group(s) of the carbonyl group on the alkyl group for R_(4a) and/or R_(5a) of the compound (I-1) is removed by hydrolysis.

Hydrolysis may be carried out in a conventional manner and, for example, the removal of the protecting groups of acetal-type and cyclic acetal-type is preferably carried out by an acidic hydrolysis, i.e. in the presence of an acid such as an inorganic acid (e.g. hydrochloric acid or sulfuric acid) or an organic acid (e.g. formic acid, acetic acid, trifluoroacetic acid or p-toluenesulfonic acid); the removal of the protecting groups of thioacetal-type, cyclic thioacetal-type and cyclic monothioacetal type is preferably carried out by hydrolysis in the presence of a heavy metal salt such as mercuric chloride or copper chloride; and the removal of the protecting group of acylal-type is preferably carried out by the above mentioned acidic hydrolysis or a basic hydrolysis, i.e. in the presence of a base such as an inorganic base (e.g. sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate) or an organic base (e.g. sodium methoxide, sodium ethoxide, potassium methoxide, potassium ethoxide, pyridine or picoline). These reactions of hydrolysis may be carried out in a suitable conventional solvent such as water, acetone, methyl ethyl ketone, dioxane, ethanol, methanol, N,N-dimethylformamide, N-methylmorpholine or dimethylsulfoxide, an optional mixture with water or a buffer solution thereof. The reaction temperature is not restrictive, and the reaction is usually conducted under cooling, at room temperature or under somewhat elevated temperature.

3. Condensation to form imino function The compound of the formula: ##STR7## wherein R₁, R₂ and R₃ are each as defined above and R_(4c) and R_(5c) are each hydrogen, lower alkyl or substituted lower alkyl in which the subsituent is hydroxyimino, hydrazono, lower alkoxyimino, hydroxy(lower)alkylimino or N'-or N,N-di-(lower)alkylamino(lower)alkylimino, provided that at least one of R_(4c) and R_(5c) is said substituted lower alkyl, may be prepared by reacting a compound of the formula: ##STR8## wherein R₁, R₂, R₃, R_(4b) and R_(5b) are each as defined above, with an amine of the formula:

    R.sub.8 -- NH.sub.2                                        (IV)

wherein R₈ is hydroxy, amino, lower alkoxy, hydroxy(lower)alkyl or N -- or N , N -di(lower)alkylamino(lower)alkyl.

According to this process the oxo group in R_(4b) and/or R_(5b) of the starting compound (I-2) is replaced by the imino group of ═N--R₈ (wherein R₈ is as defined above).

The starting compound (I-2) can be obtained by the above-mentioned hydrolysis process.

The reaction is carried out in a usual manner, for example, in the presence of a catalyst, such as an acid (e.g. hydrochloric acid, hydrobromic acid, sulfuric acid, formic acid, acetic acid, p-toluenesulfonic acid, boron trifluoride, silicon tetrachloride or titanium tetrachloride); in a basic condition realized by using the free amino-compound (IV); or an acidic or basic conventional buffer solution, and usually in a suitable conventional solvent such as water, dioxane, ethanol, methanol or dimethylformamide or an optional mixture with water thereof.

The reaction temperature is not restrictive, and the reaction is usually carried out under cooling, at room temperature or under somewhat elevated temperature. The amine (IV), which is used as a reactant, includes an N'- or N', N'-di-(lower)-alkylamino(lower)alkylamine such as N'-methyl or N',N'-dimethylamino-ethylenediamine, N'-ethyl or N',N'-diethylethylenediamine, N'-methyl or N',N'-dimethylaminotrimethylenediamine or N'-ethyl or N',N'diethylaminotrimethylenediamine; hydroxy(lower)alkylamine such as ethanolamine or propanolamine; hydroxylamine; hydrazine and lower alkoxyamine such as O-methyl-, O-ethyl-, O-propyl-, or O-isopropyl-hydroxyamine. And these amines may be used in the form of salt with an acid such as an inorganic acid (e.g. hydrochloric acid or sulfuric acid) or an organic acid (e.g. acetic acid).

4. Dehydration The compound of the formula: ##STR9## wherein R₁, R₂ and R₃ are each as defined above and R_(4d) and R_(5d) are each hydrogen, lower alkyl, cyano or ω-cyano(lower)alkyl, provided that, when one of R_(4d) and R_(5d) is hydrogen or lower alkyl, the other is always cyano or ω-cyano(lower)alkyl, and when R_(4d) and R_(5d) are not hydrogen or lower alkyl, both of them are a group selected from cyano or ω-cyano(lower)alkyl, or R_(4d) is hydrogen or lower alkyl and R₃ and R_(5d) are combined together to form a group of the formula: ##STR10## may be prepared by treating the compound of the formula: ##STR11## wherein R₁, R₂ and R₃ are each as defined above and R'_(4c) and R'_(5c) are each hydrogen, lower alkyl or ω-hydroxyimino(lower)alkyl, provided that at least one of R'_(4c) and R'_(5c) is ω-hydroxyimino(lower)alkyl, with a dehydrating agent.

The starting compound (I-3') can be obtained by the above-mentioned condensation process.

Suitable example of the dehydrating agent may be organic or inorganic conventional ones such as an acid (e.g. sulfuric acid, phosphoric acid, polyphosphoric acid, formic acid, acetic acid, ethane sulfonic acid or p-tolene sulfonic acid), an acid anhydride (e.g. acetic anhydride, benzoic anhydride or phthalic anhydride), an acid halide (e.g. acetyl chloride, benzoyl chloride, trichloroacetylchloride, mesyl chloride, tosylchloride, ethyl chloroformate or phenylchloroformate), an inorganic halogen compound (e.g. thionylchloride, phosphorus pentachloride, phosphorus oxychloride, phosphorus tribromide, stannic chloride or titanium tetrachloride), a carbodiimide (e.g. N,N'-dicyclohexylcarbodiimide or N-cyclohexyl-N'-morpholinoethylcarbodiimide), N,N'-carbonyldiimidazole, pentamethyleneketene-N-cyclohexylimine, ethoxyacetylene, 2-ethyl-7-hydroxyisoxazolium salt, another phosphorus compound (e.g. phosphorus pentoxide, polyphosphoric acid ethylester, triethylphosphate or phenylphosphate) or the like. When an acid is used as the dehydrating agent, the reaction may be conveniently conducted in the presence of its alkali metal salt (e.g. sodium salt or potassium salt), or the like.

This reaction is usually carried out in a conventional solvent such as diethyl ether, dimethylformamide, pyridine, acetic acid, formic acid, benzene, carbon tetrachloride, chloroform, methylene chloride, tetrahydrofuran, dioxane, and the like, and usually carried out at room temperature or under heating, and the reaction temperature is not restrictive to the above.

According to this process, the terminal --CH═N--OH function in R'_(4c) and/or R'_(5c) of the starting compound (I-3') is transformed into cyano function in the resultant compound (I-4), and further there tends to produce the compound of the formula: ##STR12## wherein R₁ and R₂ are each as defined above and R"_(4c) is hydrogen or lower alkyl when the starting compound (I-3') wherein R'_(5c) is hydroxyiminomethyl is treated, for example, in rather highly acidic condition. The compound (I-4') and the process for preparation thereof are also included in the scope of this invention.

This dehydration process can be also carried out successively to the foregoing condensation process without any isolation of the compound (I-3'). This case is also included in the scope of this invention.

5. Reduction of oxo- or imino- function The compound of the formula: ##STR13## wherein R₁, R₂ and R₃ are each as defined above and R_(4e) and R_(5e) are each hydrogen, lower alkyl or substituted lower alkyl in which the substituent is hydroxy, hydrazino, hydroxy(lower)-alkylamino or N'- or N',N'-di(lower)alkylamino(lower)alkylamino, provided that at least one of R_(4e) and R_(5e) is said substituted lower alkyl or R_(4e) is hydrogen or lower alkyl and R₃ and R_(5e) are combined together to form ##STR14## (wherein R₆ and R₇ are each as defined above), can be prepared by reducing the compound of the formula: ##STR15## wherein R₁, R₂ and R₃ are each as defined above and R'_(4b) and R'_(5b) are each hydrogen, lower alkyl or substituted lower alkyl in which the substituent is oxo, hydrazono, hydroxy(lower)-alkylimino or N'- or N',N'-di(lower)alkylamino(lower)alkylimino, provided that at least one of R'_(4b) and R'_(5b) is said substituted lower alkyl.

The starting compound (I-2') can be prepared by either of the above-mentioned process hydrolysis or condensation.

The reduction can be carried out by a conventional manner for reduction of oxo or imino to hydroxy or amino, respectively, for example, reduction with a reducing agent such as an alkali metal hydride (e.g. lithium borohydride, sodium borohydride, potassium borohydride or sodium cyanoborohydride) or catalytic reduction for which catalyst may be palladium carbon, palladium chloride or rhodium carbon and the like in a suitable conventional solvent. Examples of such solvents are water, methanol, ethanol, isopropanol, dimethylformamide, and the like. The reaction temperature is not restrictive, and the reaction is usually carried out under cooling, at room temperature or at somewhat elevated temperature. And, the method of reduction may be optionally selected according to the kind of the starting compound (I-2').

According to this process, each oxo- or imino-function in the starting compound (I-2') is transformed into the hydroxy- or amino-function, respectively, in the resultant compound (I-5), and further, the compound of the formula: ##STR16## wherein R₆ is as defined above and R_(4e) is hydrogen or lower alkyl, and the compound of the formula: ##STR17## wherein R₇ is as defined above and R_(4e) is hydrogen or lower alkyl, can be produced simultaneously via the compound (I-5) wherein R_(5e) is hydroxymethyl (when R₆ is hydrogen), 1-hydroxyethyl (when R₆ is methyl), 2-(N',N'-diethylamino)ethylaminomethyl (when R₇ is 2-(N,N-diethylamino)ethyl) or 2-hydroxyethylaminomethyl (when R₇ is 2-hydroxyethyl), respectively.

These cases are also included in the scope of this invention.

6 Acylation of hydroxy function The compound of the formula: ##STR18## wherein R₁, R₂ and R₃ are each as defined above and R_(4f) and R_(5f) are each hydrogen, lower alkyl or acyloxy(lower)alkyl, provided that at least one of R_(4f) and R_(5f) is acyloxy(lower)alkyl, can be prepared by reacting the compound of the formula: ##STR19## wherein R₁, R₂ and R₃ are each as defined above and R'_(4e) and R'_(5e) are each hydrogen, lower alkyl or hydroxy(lower)alkyl, provided that at least one of R'_(4e) and R'_(5e) is hydroxy(lower)alkyl, with an acylating agent of the formula:

    R.sub.9 -- OH                                              (V)

wherein R₉ is acyl, or its reactive derivative.

The starting compound (I-5') can be prepared in the above-mentioned reduction process.

Suitable examples of acyl for R₉ are lower alkanoyl which may be substituted with carboxy, esterified carboxy, N- or N,N-di-substituted amino or aryloxy, aroyl and the like.

Suitable acylating agent (V) includes lower alkanoic, acid such as formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid or pivalic acid; carboxy(lower)alkanoic acid, i.e. di- or poly-basic carboxylic acid such as malonic acid, succinic acid, adipic acid, glutaric acid, pimeric acid or suberic acid; esterified carboxy(lower)alkanoic acid, i.e. a half ester of the preceding di- or poly-basic carboxylic acid such as a respective half lower alkyl ester (e.g. methyl ester, ethyl ester or propyl ester); N- or N,N-di-substituted amino(lower)-alkanoic acid such as N- or N,N-di-(lower)alkylamino(lower)-alkanoic acid (e.g. N-methyl(or N,N-dimethyl)amio-acetic acid, 1(or 2)- N-ethyl(or N,N-diethyl)amino!propionic acid or 1(or 2)- N-methyl-N-ethylamino!propionic acid) or N-lower alkyl-N-ar(lower)alkylamino(lower)alkanoic acid (e.g. 1- (or 2)- N-methyl-N-benzylamino! propionic acid); aryloxy(lower)alkanoic acid such as phenoxyacetic acid, tolyloxyacetic acid, 2(or 3 or 4)-chlorophenoxyacetic acid, 2- 2(or 3 or 4)-chlorophenoxy!propionic acid, 2(or 3 or 4)-nitrophenoxyacetic acid or 2(or 3 or 4)-methoxy-phenoxyacetic acid); and aromatic carboxylic acid such as benzoic acid, naphtholic acid, toluic acid; and the like.

The reactive derivative at the carboxy group of the compound (V) may be its acid halide such as acid chloride; acid anhydride; active amide; azide; or reactive ester such as methyl ester, ethyl ester, cyanomethyl ester, p-nitrophenyl ester or pyranyl ester.

The reaction can be preferably carried out in the presence of a base such as an organic base (e.g. sodium hydroxide, potassium hydroxide, sodium bicarbonate, potassium bicarbonate, sodium carbonate or potassium carbonate) or an organic base (e.g. N-methylpiperidine, triethylamine, pyridine, N-methylmorphorine or N,N-dimethylaniline), and a suitable conventional solvent such as pyridine, ether, dioxane, acetone, chloroform, methylene chlorie, tetrahydrofuran, dimethylformamide, benzene or water. The reaction temperature is not restrctive, and the reaction is usually carried out under cooling, at room temperature or under somewhat elevated temperature. If necessary, there may be used a conventional condensing agent such as phosphorus oxychloride, thionylchloride, N,N'-dicyclohexylcarbodiimide, N-cyclohexyl-N'-morphorinoethylcarbodiimide, pentamethyleneketene-N-cyclohexylimine, alkoxyacetylene, 2-ethyl-7-hydroxyisoxazolium salt, 2-ethyl-5-(m-sulfophenyl)isoxazolium hydroxide or 6-chloro-1-tosyloxybenzotriazole.

7. Oxidation of alcohol to aldehyde

The compound of the formula: ##STR20## wherein R₁, R₂ and R₃ are each as defined above and R_(4g) and R_(5g) are each hydrogen, lower alkyl, formyl or ω-formyl(lower)alkyl, provided that, when one of R_(4g) and R_(5g) is hydrogen or lower alkyl, the other is always formyl or ω-formyl(lower)alkyl, and R_(4g) and R_(5g) are not hydrogen or lower alkyl, both of them are a group selected from formyl and ω-formyl(lower)alkyl, may be also prepared by oxidizing the compound of the formula ##STR21## wherein R₁, R₂ and R₃ are each as defined above and R"_(4e) and R"_(5e) are each hydrogen, lower alkyl, or ω-hydroxy(lower)alkyl, provided that at least one of R"_(4e) and R"_(5e) is ω-hydroxy(lower)alkyl.

The starting compound (I-5") can be prepared in the above-mentioned reduction process.

The oxidation can be carried out by any conventional method which selectively oxidize a primary alcohol function to the corresponding formyl function without any adverse influence on the other parts of the compound (I-b 5").

A suitable oxidation is carried out by reacting the starting compound (I-5") with an organic sulfonic acid or its reactive derivative, preferably under warming and in the presence of a base, with or without a solvent. This reaction may be proceeded via the organic sulfonic acid ester of the compound (I-5") as an intermediate which may be produced in the course of the reaction.

Suitable organic sulfonic acid may be methanesulfonic acid, p-toluenesulfonic acid, p-nitrophenylsulfonic acid and the like, and its reactive derivative and the base can be referred to those of the compound (V) as mentioned in the preceding acylation process.

8. Pyrolytic ring closure

The compound of the formula: ##STR22## wherein R₁ and R₂ are each as defined above, R_(4h) is hydrogen or lower alkyl, and R₃ and R_(5h) are combined together to form a group of the formula: ##STR23## in which R₆ is as defined above, may be prepared by heating in neat or in a conventional solvent the compound (I-5) wherein R_(4e) is hydrogen or lower alkyl and R_(5e) is hydroxymethyl, or the compound (I-3) wherein R_(4c) is hydrogen or lower alkyl and R_(5c) is hydrazonomethyl, respectively.

A suitable conventional solvent includes water, methanol, ethanol, isopropanol, butanol, dioxane, benzene, toluene, dimethylformamide, tetrahydrofuran, or a conventional buffer solution and the like. The reaction can be accelerated by the addition of a catalytic or more amount of an organic or inorganic base such as trialkylamine (e.g. trimethylamine or triethylamine), pyridine, alkali metal compound (e.g. sodium hydroxide, potassium hydroxide, sodium bicarbonate or potassium bicarbonate) and the like, or an organic or inorganic acid such as acetic acid, p-toluenesulfonic acid, hydrochloric acid, sulfuric acid, boron trifluoride, silicon tetrachloride, titanium tetrachloride and the like. The reaction temperature is not so much restrictive, and the reaction is preferably carried out under warming or heating.

9. Other transformations

(1) The compound (I) wherein R₁, R₂ and R₃ are as defined above and R₄ and R₅ are each hydrogen, lower alkyl or lower alkyl substituted with a 5 or 6-membered saturated N-containing heterocyclic-1-yl which may have hydroxy, lower alkyl or hydroxy(lower)alkyl, provided that at least one of R₄ and R₅ is said substituted lower alkyl, can be prepared by subjecting the compound (I-5') to halogenation of the hydroxy function, whereby a halo-compound is provided, followed by substitution reaction with a 5 or 6-membered saturated imino-containing heterocyclic compound.

The first halogenation reaction can be carried out by reacting halogenating agent such as conventional one (e.g. thionyl chloride, phosphorus tribromide, phosphorus pentachloride or phosgene) and other one which comprises a combination of phosphorus compound such as triphenyl phosphine or tri(lower)alkyl phosphite (e.g. trimethyl phosphite or triethyl phosphite) and a polyhalo(lower)alkane such as carbon tetrachloride or carbon tetrabromide in a suitable solvent. Examples of the solvents may be carbon tetrachloride, chloroform, methylene chloride, benzene and the like. This reaction is preferably carried out in around neutral conditions, therefore, the latter combination agent is the most preferable one. On the contrary, in case of the former conventional agent, it may be usually carried out on mantaining neutrality of the reaction medium, for example, by neutralizing with a base or scavenging the resulting acidic substances from the halogenating agent in the course of reaction performed. The reaction temperature is usually varied in accordance with the kind of halogenating agent, and therefore, the reaction is preferably carried out at somewhat elevated temperature (e.g. under warming or heating) in case of the latter combination agent, and at much more milder temperature (e.g. under cooling or warming) in case of the former conventional agent, and preferably under anhydrous conditions.

The second substitution reaction is carried out in a substantially similar manner to that of aforementioned acylation process in the presence or absence of a base. The reaction can be carried out in a suitable solvent such as chloroform, methylene, chloride, benzene, acetone, ether, tetrahydrofuran, dimethylformamide, methanol, ethanol or propanol. The reaction temperature is not restrictive, and the reaction is usually carried out at room temperature or at an elevated temperature (e.g. under warming or heating). According to this method, the hydroxy(lower)alkyl group for R'_(4e) and/or R'_(5e) of the compound (I-5') is transformed at first into the halo(lower)alkyl group and then into the lower alkyl substituted with 5 or 6-membered saturated N-containing heterocyclic-1-yl group for R₄ and/or R₅ of the compound (I).

(2) The compound (I) wherein at least one of R₂ and R₃ is N- or N,N-di-substituted amino(lower)alkoxycarbonyl can be prepared by reacting the corresponding compound (I) wherein at least one of R₂ and R₃ is halo(lower)alkoxycarbonyl with a N- or N,N-di-substituted amine in accordance with the substantially same manner as that of the above-mentioned substitution reaction in 1).

(3) The compound (I) wherein at least one of R₂ and R₃ is hydroxy(lower) alkoxycarbonyl can be prepared by subjecting the corresponding compound (I) wherein at least one of R₂ and R₃ is halo(lower)alkoxycarbonyl to hydrolysis substantially in the same method as that of the afore-mentioned hydrolysis process.

(4) The compound (I) wherein R₁, R₂ and R₃ are each as defined above and R₄ and R₅ are each hydrogen, lower alkyl or substituted lower alkyl selected from gem-di-(lower)alkoxy)(lower)alkyl; gem-lower alkylenedioxy(lower)alkyl; gem-di-(lower)alkylthio(lower)alkyl or gem-(lower)alkylene-dithio(lower)alkyl, provided that at least one of R₄ and R₅ is said substituted lower alkyl can be also prepared by reacting the corresponding compound (I-2) with a hydroxy compound such as lower alkanol (e.g. methanol, ethanol or propanol) or lower alkane diol (e.g. ethylene glycol, propylene glycol, 2,3-butane diol or 1,3-propane diol); a thiol compound such as lower alkanethiol (e.g. methanethiol or ethanethiol) or lower alkane dithiol (e.g. ethanedithiol, 1.2-propanedithiol, 2,3-butanedithiol or 1,3-propanedithiol).

This reaction preferably carried out in the presence of catalytic amount of an organic or inorganic acid such as hydrochloric acid, sulfuric acid, acetic acid, boron trifluoride, zinc chloride or p-toluenesulfonic acid,

(5) The compound (I) wherein R₁, R₂ and R₃ are each as defined above and R₄ and R₅ are each hydrogen, lower alkyl or cyano(lower)alkyl, provided that at least one of R₄ and R₅ is cyano(lower)alkyl can be prepared by reacting the halo-compound obtained in the above transformation (1) with a compound of the formula: R₁₀ -CN wherein R₁₀ is hydrogen or a metal.

Suitable metals for R₁₀ are alkali metal such as sodium or potassium, alkaline earth metal such as magnesium or calcium, heavy metal such as mercury or silver and the like.

The reaction is usually carried out at room temperature or under heating in a suitable solvent such as water, methanol, ethanol, butanol chloroform, benzene, toluene, N,N-dimethylformamide, dimethylsulfoxide, N-methylmorpholine, pyridine or other conventional solvent.

In accordance with the present invention, the product which is given during the reaction is separated and isolated from the reaction mixture by methods commonly used for this purpose, and may be subjected to routinely used purification procedures, for instance, to recrystallization from an appropriate solvent or a mixture of such solvents.

The compound (I) thus obtained wherein at least R₂ and R₃ or R₄ and R₅ are not just same each other, includes stereoisomers due to the presence of at least one asymmetric carbon atom at the fourth position of the 1,4-dihydropyridine nucleus and can exist as each optical isomer or a racemic mixture. And further some of the copound (I) which has not less than two asymmetric carbon atoms in its molecule may exist as each diastereomer(s) or the mixture thereof. The mixture of the diastereomers can be resolved to each racemic compound by conventional resolution methods such as chromatography or fractional recrystallization and the like and the racemic compound can be resolved into each optical isomer by a conventional method for racemic resolution such as a resolution by fractional recrystallization of a salt of the racemic compound with an optically active acid, e.g., tartaric acid or camphor sulfonic acid.

The compound (I) is possessed of vasodilating activity and useful for therapeutical treatment in hypertension and cardiovascular diseases such as coronary insufficiency, angina pectoris or myocardial infarction.

The compositions of this invention comprise, as an active ingredient, the 1,4-dihydropyridine derivatives (I) in an amount of about 0.1 mg. to about 500 mg., preferably about 1 mg. to about 50 mg. per daily oral dosage unit, with IV dosage being 10 to 25% of oral.

One skilled in the art will recognize that in determining the amounts of the active ingredient in the claimed dosage unit form, the activity of the ingredient as well as the size of the host animal must be considered. That is, on mg./kg. oral basis (see above ratio for IV), the amount of the active ingredient in the compositions will be about μg/kg, to about 10 mg./kg. and more, preferably about 0.5 mg./kg. to about 5 mg./kg. For administration purpose of this pharmaceutical composition, the active ingredients may be usually formed as tablet, granule, powder, capsule, suppository, suspensions, solutions and the like. A pharmaceutical carrier or diluent includes solid or liquid non-toxic pharmaceutically acceptable substances. Exemplar of solid or liquid carriers or diluents are lactose, magnesium stearate, terra alba sucrose, corn starch, talc, stearic acid, gelatin, agar, pectin, acacia, peanut oil, olive oil or sesame oil, cacao butter or the like. Similarly, the carrier or diluent may include a time delay material such as glyceryl monostearate or glyceryl distearate alone or with a wax.

A wide variety of pharmaceutical forms can be employed. Thus, if a solid carrier is used, the preparation can be tabletted, placed in a hard gelatin capsule or in the form of a troche or lozenge.

The pharmacological activity of the 1,4-dihydropyridines of the formula (I) is demonstrated by standard procedures, that is, by administering intravenously the following test 1,4-dihydropyridines to dogs anesthetized with pentobarbital and recording the coronary blood flow. The test results are given below: ##STR24## Table. Increase of coronary blood flow (%)

The values indicate percentages compared to control 29.5±5.5 ml/min.!.

    ______________________________________                                         Dose μg/kg                                                                  Compound     64        250       1000                                          ______________________________________                                         A            169       118       dead                                          B            190       174       155                                           C            214       168       175                                           D            171       195       179                                           E            185       215       144                                           ______________________________________                                    

Compound A is known as the generic name "Nifedipine" and already marketed as a coronary vasodilator.

The following Examples are given merely for the purpose of illustrating the syntheses of some specific object compounds of the present invention, but not of limiting the same thereto.

EXAMPLE 1

(1) A solution of 2-chlorobenzaldehyde (1.0543 g), ethyl 4,4-diethoxyacetoacetate (1.6477 g) and piperidine (1 to 2 drop(s)) in benzene (30 ml) was refluxed under azeotropic dehydration for 4.5 hours. After cooling, the resultant solution was washed with water and dried. The solvent was removed from the solution to give orange oil (2.7196 g) of ethyl 2-(2-chlorobenzylidene)-4,4-diethoxyacetoacetate. The mixture of the compound obtained above and ethyl 3amino-4,4-diethoxycrotonate (1.6580 g) was heated with stirring at about 100° C. for 1.5 hours and about 120° C. for 8 hours. After cooling, the reaction mixture was dissolved in ethyl acetate. The solution was washed with water and dried, and then the solvent was removed from the solution to give orange oil (4.21 g) of diethyl 2,6-bis(diethoxymethyl)-4-(2-chlorophenyl)-1,4-dihydropyridine-3,5-dicarboxylate. The product was purified by a column chromatography on silica gel with an eluent (benzene: ethyl acetate = 10:1) to give pure product.

I.R. Spectrum (Film) ν (cm⁻¹): 3430, 1695, 1610, 1487, 1472, 1368, 1273, 1200, 1093, 1059, 755.

N.M.R. Spectrum (δ, CDCl₃) ppm: 1.22 (18H, t, J=7Hz), 3.3 to 3.9 (8H, m), 4.08 (4H, q, J=7Hz), 5.55 (1H, s), 6.14 (2H, s), 6.9 to 7.5 (4H, m), 7.90 (1H, broad s).

(2)-(1) A solution of 2-chlorobenzaldehyde (14.0570 g), ethyl 4,4-diethoxyacetoacetate (21.8240g) and piperidine (1 ml) in benzene (100 ml) was refluxed under azeotropic dehydration for 4 hours. The resultant solution was washed with water, dried and concentrated to give oily ethyl 2-(2-chlorobenzylidene)-4,4-diethoxyacetoacetate. The mixture of the compound obtained above and ethyl 3aminocrotonate (12.92 g) was heated in an oil bath (about 100° C.) for 8 hours. The reaction mixture was dissolved in ethyl acetate, washed with water, dried and then the solvent was removed to give crude oil (52.4 g). The oil was purified by column chromatography on silica gel with an eluent (benzene:ethyl acetate = 20:1) to give diethyl 2-methyl-4-(2-chlorophenyl)-6-diethoxymethyl-1.4-dihydropyridine-3,5-dicarboxylate, which was recrystallized from n-hexane to give the pure crystals (20.2445 g), m.p. 75° to 77° C.

(2)-(2) A solution of 2-chlorobenzaldehyde (1.4057 g), ethyl acetate (1.3014 g) and piperidine (5 drops) in benzene (10 ml) was refluxed under azeotropic dehydration for 5 hours. After cooling, to the resultant solution was added benzene, and the solution was washed with water twice and dried. The solvent was removed from the resultant solution to give yellowish oil of ethyl 2-(2-chlorobenzylidene)acetoacetate (2.7351 g). The mixture of the compound obtained above and ethyl 3-amino-4,4diethoxycrotonate (2.17 g) was heated at about 120° C. with stirring for 4 hours. After cooling, the resultant oil was dissolved in diethyl ether, washed with water and saturated aqueous solution of sodium chloride in turn and then dried. The solution was concentrated under reduced pressure to give a reddish oil (4.5133 g). The product was purified by column chromatography on silica gel with an eluent (benzene:ethyl acetate = 20:1) to give yellowish oil of diethyl 2-methyl-4-(2-chlorophenyl)-6-diethoxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (2.25 g). The product was crystallized in n-hexane and the crystals were collected by filtration, which were identified with the authentic sample.

(3) A mixture of 2-chlorobenzaldehyde (2.81 g), methyl 4,4-dimethoxy-3-oxovalerate (3.81g) and piperidine (0.2 ml) in benzene (20 ml) was refluxed under azeotropic dehydration for 7.5 hours. A small amount of benzene was added to the reaction mixture and the resultant solution was washed with water and dried over magnesium sulfate. The solvent was removed from the solution to give a reddish oil (7.04 g) of methyl 2-(2-chlorobenzylidene)-4,4-dimethoxy-3-oxovalerate. The mixture of the oily product (6.39 g) obtained above and methyl 3-aminocrotonate (2.33 g) was heated at 132° C. for 3.5 hours, allowed to stand and then dissolved in ethyl acetate. The resultant solution was washed with water and an aqueous sodium chloride solution, and dried over magnesium sulfate. The solvent was removed from the solution under reduced pressure to give a viscous and brown oil (8.28 g). This oil was subjected to column chromatography on silica gel with an eluant (a mixture of 20 parts of benzene and one part of ethyl acetate by volume) to give an oily substance (5.26 g). This substance was dissolved in a mixture of ethyl acetate and diethyl ether and the solvent was removed under reduced pressure to give colorless power (1.0625 g). This powder was recrystallized from a mixture of n-hexane and ethyl acetate to give faint yellow granules of dimethyl 2-methyl-4-(2-chlorophenyl)-6-1,1-dimethoxyethyl-1,4- dihydropyridine-3,5-dicarboxylate, m.p. 145° to 146° C.

(4)-(1) A solution of 2-nitrobenzaldehyde (9.0672 g), ethyl 4,4-diethoxyacetoacetate (13.0944 g) and piperidine (1ml) in benzene (45 ml) was refluxed under azeotropic dehydration for 3 hours. To the resultant solution was added water, and the solution was extracted with diethyl ether. The extract was washed three times with water, dried and then the solvent was removed under reduced pressure to give ethyl 2-(2-nitrobenzylidene)-4,4-diethoxyacetoacetate. The mixture of the compound obtained above and ethyl 3-aminocrotonate (7.7496 g) was heated in an oil bath (95° to 100° C.) for 8 hours. The resultant mixture was extracted with diethyl ether, and the extract was washed with water and dried. The solvent was removed from the extract. The residue was purified by column chromatography on silica gel with an eluent (benzene : ethyl acetate = 20:1) to give oily diethyl 2-methyl-4-(2-nitrophenyl)-6-diethoxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (19.3 g). The product was crystallized in n-hexane and the crystals were collected by filtration and then recrystallized from a mixture of n-hexane and diethyl ether to give the pure compound, m.p. 80° to 81.5° C.

N.M.R. Spectrum (δ, CDCl₃) ppm :1.16 (3H, t, J=7Hz), 1.18 (3H, t, J=7Hz), 1.25 (6H, t, J=7Hz), 2.37 (3H, s), 3.4 to 4.4 (8H, m), 5.92 (1H, s), 6.20 (1H; s); 6.67 (1H, broad s), 7.0 to 7.8 (4H, m)

(4)-(2) A solution of 2-nitrobenzaldehyde (3.0224 g), ethyl 4,4-diethoxyacetoacetate (4.3650 g) and piperidine (240mg) in benzene (12 ml) was refluxed under azeotropic dehydration for 80 minutes. The reaction mixture was allowed to stand to cool, and ethyl acetate was added thereto. The mixture was washed with water twice and dried. The solvent was removed to give an orange-yellow oil (6.88 g). The oil was kept in a refrigerator overnight to give crystals. The crystals were collected by filtration to give faint yellow crystals (3.3690 g), which were recrystallized from diisopropyl ether to give colorless granules (2.2479 g) of ethyl 2-(2-nitrobenzylidene)-4,4-diethoxyacetoacetate, m.p. 66° to 67.5° C. This product is one of the two isomers of ethyl 2-(2-nitrobenzylidene)-4,4-diethoxyacetoacetate and shows signal at 5.23 ppm(methine proton) and 8.31 ppm (olefinic proton) on N.M.R. spectrum (δ, CDCl₃). The filtrate was condensed and the resultant brown oil, which comprises the two isomers of ethyl 2-(2-nitrobenzylidene)-4,4-diethoxyacetoacetate in the ratio approximately 1:1 and shows signals of 4.93 and 5.23 ppm (methine proton) and 8.17 and 8.31 ppm (olefinic proton) on N.M.R. spectrum (δ, CDCl₃).

A mixture of the above obtained crystals (2.4497 g) and ethyl 3-aminocrotonate (1.3508 g) was heated at 75° to 82° C. with stirring under slightly reduced pressure for four hours and further heated at 105° to 108° C. for five hours. The reaction mixture was cooled and crystallized. The resultant crystals were recrystallized from a mixture of diisopropyl ether and n-hexane to give crystals (0.5128 g) of diethyl 2-methyl-4-(2-nitrophenyl)-6-diethoxymethyl-1,4-dihydropyridine-3,5-dicarboxylate which was identified with the product of the above Example (1-4 )-(1).

(5) A solution of 3-nitrobenzaldehyde (2.27 g), ethyl 4,4-diethoxyacetoacetate (3.28 g) and piperidine (0.2 ml) in benzene (15 ml) was refluxed under azeotropic dehydration for 3 hours. The resultant solution was washed three times with water and dried over magnesium sulfate. The solvent was removed from the reaction solution to give oily ethyl 2-(3-nitrobenzylidene)-4,4-diethoxyacetoacetate (6.0 g). The mixture of the compound obtained above and ethyl 3-aminocrotonate (1.94 g) was heated at about 95° to 100° C. for 7 hours and then at about 120° C. for 1.5 hours with stirring. After cooling, the resultant oil was extracted with ethyl acetate and the extract was washed with water and dried. The solvent was removed from the resultant solution to give an oil (7.8 g). The product was purified by column chromatography on silica gel with an eluent (benzene : ethyl acetate = 20:1) to give the pure product of diethyl 2-methyl-4-(3-nitrophenyl)- 6-diethoxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (4.65 g).

I.R. Spectrum (Film) ν (cm⁻¹): 3400, 1690, 1615, 1530, 1480, 1350, 1280, 1200, 1090, 920, 765.

N.M.R. Spectrum (δ, CDCl₃) ppm : 1.23, 1.26 (12H, t, t, J=7Hz) 2.4 (3H, s), 3.5 to 3.86 (4H, m), 4.11 (4H, q J=7Hz), 5.16 (1H, s), 6.82 (1H, broad), 7.25 to 8.16 (4H, m).

(6) A mixture of ethyl 2-(2-trifluoromethylbenzylidene)4,4-diethoxyacetoacetate (7.48 g) and ethyl 3-aminocrotonate (2.582 g) was heated at 130° C. for 5 hours. The resultant mixture was dissolved in ethyl acetate and solution was washed with water twice, dried over magnesium sulfate and concentrated under reduced pressure to give a red oil (9.8 g). The oil was subjected to column chromatography on silica gel with an eluent (a mixture of 20 parts benzene and one part of diethyl ether by volume) to give an oily substance. This substance turned into crystals, which were recrystallized from a mixture of n-hexane and diethyl ether to give crystals of diethyl 2-methyl-4-(2-trifluoromethylphenyl)-6-diethoxymethyl-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 82420 to 83° C.

(7) A solution of 2-methoxybenzaldehyde (2.7228 g), ethyl 4,4-diethoxyacetoacetate (4.3648 g) and piperidine (4 or 5 drops) in benzene (20 ml) was refluxed under azeotropic dehydration for 3 hours. The resultant solution was washed with water and dried. The solvent was removed from the extract to give oily ethyl 2-(2-methoxybenzylidene)-4,4-diethoxyacetoacetate. The mixture of the compound obtained above and ethyl 3-aminocrotonate (2.5832 g) was heated in an oil bath (about 100° C.) for 7 hours. After cooling, the reaction mixture was extracted with diethyl ether, and the extract was washed with water twice and dried over magnesium sulfate. The solvent was removed to give a red oil. The oil was purified by a column chromatography on silica gel with an eluent (benzene : ethyl acetate = 20:1) to give diethyl 2-methyl-4-(2-methoxyphenyl)-6 -diethoxymethyl-1,4-dihydropyridine3,5-dicarboxylate (5.0779 g). The product was recrystallized from n-hexane to give pale yellowish prisms, m.p. 105 to 107° C.

(8) A mixture of 2-chloro-5-nitrobenzyaldehyde (3.73 g), ethyl 4,4-diethoxyacetoacetate (4.365 g) and piperidine (272.5 mg) in benzene (10 ml) was refluxed under azeotropic dehydration for 1.5 hours. To the mixture was added ethyl acetate, and the resultant mixture was washed three times with water and then with an aqueous solution of sodium chloride, and dried over magnesium sulfate. The solvent was removed under reduced pressure to give a reddish brown oil (7.87 g) of ethyl 2-(2-chloro-5-nitrobenzylidene)-4,4-diethoxyacetoacetate. The mixture of thus obtained reddish brown oil and ethyl 3-aminocrotonate (3.48 g) was heated with stirring at 105° to 107° C. in an oil bath for 4.5 hours. The resultant mixture was extracted with ethyl acetate, and the extract was washed with water three times and then with an aqueous solution of sodium chloride, and dried over magnesium sulfate. After removal of the solvent from the extract, the obtained residue (10.87 g) was subjected to column chromatography on silica gel with an eluent (a mixture of 20 parts of chloroform and one part of ethyl acetate by volume). The fractions were checked with thin-layer chromatography and crystals (6.02 g) were obtained by removing the solvent from the fraction containing the designated substance. The crystals were recrystallized from a mixture of diethyl ether and n-hexane to give crystals of diethyl 2-methyl-4-(2-chloro-5 -nitrophenyl)-6-diethoxymethyl-1,4-dihydropyridine3,5-dicarboxylate, m.p. 117° to 118° C.

(9) A solution of thiophene-2-carbaldehyde (2.2430 g), ethyl 4,4-diethoxyacetoacetate (4.3648 g) and piperidine (4 drops) in benzene (20 ml) was refluxed under azeotropic dehydration for 4.5 hours. After cooling, to the resultant solution was added diethyl ether, and the solution was washed with watr and dried. The solvent was removed from the reaction mixture to give oily ethyl 2-(2-thenylidene)-4,4-diethoxyacetoacetate. The mixture of the compound obtained above and ethyl 3-aminocrotonate (2.6 g) was heated in an oil bath (about 100° C.) for 7.5 hours. The resultant mixture was dissolved in diethyl ether, washed with water and dried. The solvent was removed to give brown oil (9.0 g). The oil was purified by column chromatography on silica gel with an eluent (benzene : ethyl acetate = 20:1) to give diethyl 2-methyl-4-(2-thienyl)-6-diethoxymethyl-1,4-dihydropyridine-3,5-dicarboxylate. The product was recrystallized from n-hexane to give yellowish crystals (2.2056 g), m.p. 77° to 77.5° C.

(10) To a mixture of 2-furaldehyde (2.88 g) and ethyl 4,4-diethoxyacetoacetate (6.55 g) in benzene (15 ml) was added each one fourth portion of piperidine (408 mg) with an interval of 15 minutes under refluxing with azeotropic dehydration. Thus obtained mixture was refluxed for another 30 minutes. To the reaction mixture was added ethyl acetate, and the resultant mixture was washed with water three times and then with an aqueous solution of sodium chloride and dried over magnesium sulfate. The solvent was removed to give a reddish brown oil (9.47 g) of ethyl 2-(2-furfurylidene)-4,4-diethoxyacetoacetate. Then the mixture of the oil gained above and ethyl 3-aminocrotonate was heated at 105° C. under stirring for 7 hours. The resultant mixture was extracted with ethyl acetate, and the extract was washed with water and an aqueous solution of sodium chloride and then dried over magnesium sulfate. After removal of the solvent, the resultant oil was purified by column chromatography on silica-gel with an eluent (a mixture of 20 parts of chloroform and one part of ethyl acetate by volume) and crystallized from n-hexane (3 ml). The obtained crystals were washed with n-hexane to result crystals (7.05 g). The resultant crystals (500 mg) were recrystallized from n-hexane to give crystals (450 mg) of diethyl 2-methyl-4-(2-furyl)-6-diethoxymethyl-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 59° to 60° C.

(11) A mixture of 2-nitrobenzaldehyde (3.02 g), 2-ethoxyethyl acetoacetate (3.48 g) and piperidine (272.5 mg) in benzene (10 ml) was refluxed under azeotropic dehydration for 1.5 hours. The mixture was washed with water three times and with an aqueous solution of sodium chloride, dried over magnesium sulfate and concentrated. To the resultant oil of 2-ethoxyethyl 2-(2-nitrobenzylidene)acetoacetate was added ethyl 3-amino-4,4-diethoxycrotonate (4.77 g) and the mixture was heated at 110° C. under stirring for 5 hours. The reaction mixture was extracted with ethyl acetate and the extract was washed with water three times and dried over magnesium sulfate. After removal of the solvent, the resultant brown oil was purified by column chromatography with an eluent (a mixture of ten parts of benzene and one part of ethyl acetate by volume) to give an oil (3.18 g) of 2-ethoxyethyl 2-methyl-4-(2-nitrophenyl)-5-ethoxycarbonyl-6-diethoxymethyl-1,4-dihydropyridine-3-carboxylate.

I.R. Spectrum (film) ν (cm⁻¹): 3420, 1730, 1695, 1650, 1610, 1530, 1480, 1355, 1275, 1210, 1100, 860, 830, 785, 752, 715.

N.M.R. Spectrum (δ, CDCl₃) ppm : 1 to 1.37 (12H, m), 2.37 (3H, s), 3.28 to 4.3 (12H, m), 5.93 (1H, s), 6.2 (1H, s), 6.78 (1H, m), 7.23 to 7.83 (4H, m).

(12) A mixture of 2-nitrobenzaldehyde (4.536 g), 2-chloroethyl acetoacetate (4.94 g) and piperidine (110 mg) in benzene (18 ml) and acetic acid (360 mg) was refluxed for an hour under azeotropic dehydration. The reaction mixture was washed with water and dried. The solvent was distilled off to give an reddish oil of 2-chloroethyl 2-(2-nitrobenzylidene)acetoacetate, and thus obtained oil was treated with ethyl 3-amino-4,4-diethoxycrotonate (7.1 g) to give yellow granules of 2-chloroethyl 2-methyl-4-(2-nitrophenyl)- 5-ethoxycarbonyl-6-diethoxymethyl1,4 -dehydropyridine-3-carboxylate, m.p. 82° to 84° C. (recrystallized from diisopropyl ether).

(13) A mixture of 2-nitrobenzaldehyde (3.023 g), benzyl acetoacetate (3.802 g) and piperidine (272.5 mg) in benzene (10 ml), was treated in a substantially similar manner that of Example 1-11) to give a brown oil (6.94 g) of benzyl 2-(2-nitrobenzylidene)acetoacetate, which was further treated with ethyl 3-amino-4,4-diethoxycrotonate (4.34 g) to give a dark brown oil (10.3 g). This oil was purified by column chromatography on silica-gel and the resultant oil (3.8 g) was crystallized to give crystals (1.65 g) of benzyl 2-methyl-4-(2-nitrophenyl)-5-ethoxycarbonyl-6-diethoxymethyl-1,4-dihydropyridine-3-carboxylate, m.p. 103° to 103.5° C. (recrystallized from a mixture of diisopropyl ether and n-hexane).

(14) In an essentially similar manner to that of Example 1-11) given in the above, the following compounds were obtained:

Starting from a mixture of 2-nitrobenzaldehyde (3.02 g), 2-benzyloxyethyl acetoacetate (4.72 g), piperidine (272.5 mg) in benzene (10.8 ml) was obtained 2-benzyloxyethyl 2-(2-nitrobenzylidene)acetoacetate, which was further treated with ethyl 3-amino-4,4-diethoxycrotonate to give an oil (4.80 g) of 2-benzyloxyethyl 2-methyl-4-(2-nitrophenyl)-5-ethoxycarbonyl-6-diethoxymethyl-1,4 -dihydropyridine-3-carboxylate.

I.R. Spectrum (film) ν (cm⁻¹): 3400, 1700, 1650, 1610, 1530, 1480 1355, 1273, 1205, 1090, 1055, 750, 700.

N.M.R. Spectrum (δ, CDCl₃) ppm: 1.1 to 1.3 (9H, m), 2.32 (3H, s), 3.45 to 4.32 (10H, m), 4.46 (2H, s), 5.94 (1H, s), 6.2 (1H, s), 6.82 (1H, s), 7.16 to 7.74 (9H, m).

(15) In an essentially similar manner to that of Example 1- 11) given in the above, the following compounds were obtained:

Starting from a mixture of 2-nitrobenzaldehyde (3.02 g), 2-phenoxyethyl acetoacetate (4.44 g), piperidine (272.5 mg) in benzene (10.8 ml) was obtained an oil (8.0 g) of 2-phenoxyethyl 2-(2-nitrobenzylidene)acetoacetate. Thus obtained oil was treated with ethyl 3-amino-4,4-diethoxycrotonate (4.34 g) to give an oil of 2-phenoxyethyl 2-methyl-4-(2-nitrophenyl)-5-ethoxycarbonyl-6-diethoxymethyl-1,4-dihydropyridine-3-carboxylate.

I.R. Spectrum (film) ν (cm⁻¹): 3410, 1700, 1602, 1535, 1480, 1356, 1277, 1250, 1210, 1100, 1060, 755, 695.

N.M.R. Spectrum (δ, CDCl₃) ppm: 1.13 (3H, t, J=7Hz), 1.23 (6H, t, J=7Hz) 2.33 (3H, s), 3.41 to 4.47 (10H, m), 5.91 (1H, s), 6.17 (1H, s), 6.71 to 7.71 (9H, m).

(16) A mixture of 3-nitrobenzaldehyde (4.54 g), 2-ethoxyethyl acetoacetate (5.23 g) and piperidine (85.2 mg) in benzene (15 ml) was refluxed under azeotropic dehydration for 3 hours. The resultant mixture was washed with water, an aqueous solution saturated with sodium chloride and water in turn, dried and concentrated to give an oil of 2-ethoxyethyl 2-(3-nitrobenzylidene)acetoacetate. To this oily product was added ethyl 3-amino-4,4-diethoxycrotonate (6.5 g). The mixture was heated at 110° C. for about 3 hours. The reaction mixture was dissolved in ethyl acetate and washed with water twice and dried. The solvent was removed from the mixture to give an oil (15.58 g). This oil was subjected to column chromatography on silica gel with an eluent (a mixture of 10 parts of benzene and one part of ethyl acetate by volume) to give an oily substance (8.09 g). This oily substance (0.93 g) was treated with a mixture of n-hexane and diethyl ether to give crystals, which were further recrystallized from a mixture of n-hexane and diethyl ether to give yellow granules (565.2 mg) of 2-ethoxyethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-diethoxymethyl-1,4-dihydropyridine-3-carboxylate, m.p. 99° to 100° C.

(17) A mixture of 2-chloroethyl 2-(3-nitrobenxylidene)acetoacetate (16 g) and ethyl 3-amino-4,4-diethoxycrotonate (10.85 g) was heated at 100° C. for 3 hours and allowed to stand overnight at room temperature. Appearing crystals were collected by filtration to give yellow crystals (7.02 g), and then the filtrate was subjected to column chromatography on silica gel with an eluent a mixture of 20 parts of benzene and one part of ethyl acetate by volume! to give an oil (7.4 g). The oil was allowed to stand to give crystals (3.6 g) and put together with the above obtained crystals (7.02 g). These crystals were recrystallized from a mixture of n-hexane and diethyl ether to give 2-chloroethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-diethoxymethyl-1,4-dihydropyridine-3-carboxylate, m.p. 96° to 97° C.

(18) A mixture of ethyl 2-(3-hydroxybenzylidene)acetoacetate (2.1 g) and ethyl 3-amino-4,4-diethoxycrotonate (1.95 g) in n-propyl alcohol (1.5 ml) was heated at 105° C. for 4.5 hours. After removal of the solvent from the reaction mixture under reduced pressure, ethyl acetate was added to the residue. The resultant solution was washed with water twice and an aqueous sodium chloride solution in turn, and then dried over magnesium sulfate. The solvent was removed from the solution to give red oil (4.2 g). The oil was subjected to column chromatography on silica gel with an eluent a mixture of 10 parts of benzene and one part of diethyl ether by volume! to give an oily substance, which was crystallized from n-hexane to give crystals (1.5 g). These crystals (280 mg) were recrystallized from a mixture of n-hexane and diethyl ether to give crystals of diethyl 2-methyl-4-(3-hydroxyphenyl)-6-diethoxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (106.2 mg), m.p. 107° to 108° C.

(19) A solution of 2-chlorobenzaldehyde (351.4 mg), ethyl 4,4-diethoxyacetoacetate (545.6 mg) and ethyl 3-aminocrotonate (322.9 mg) in n-propanol (2 ml) was refluxed for 10 hours. The resultant solution was concentrated, and the residue was dissolved in ether, and then washed twice with water. After drying the extract over magnesium sulfate, the solvent was removed from the extract to give orange oil (1.1765 g). The oil was purified by a column chromatography on silica gel with an eluent (benzene : ethyl acetate = 20 : 1) to give oily diethyl 2-methyl-4-(2-chlorophenyl)-6-diethoxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (374.6 mg). The product was dissolved in n-hexane and allowed to stand in a refrigerator, and the precipitated crystals were collected by filtration and washed with n-hexane to give pure crystals, m.p. 75° to 77° C.

(20) A mixture of 2-(2-chlorobenzylidene)-4,4-diethoxyacetoacetate (2.42 g), ammonium acetate (1 g) and methyl propiolate (1 ml) in acetic acid (1 ml) was refluxed for minutes. The reaction mixture was poured into an aqueous solution of sodium bicarbonate and extracted twice with ethyl acetate. The ethyl acetate layer was washed with water and then with a saturated aqueous solution of sodium chloride, dried, and further concentrated. The resultant red oil was dissolved in diethyl ether and appeared crystals were filtered off. The filtrate was concentrated to give a brown oil (2.57 g). This oil was purified by column chromatography on silica-gel with an eluent (a mixture of ten parts of benzene and one part of ethyl acetate by volume). The fraction containing the designated substance was concentrated to give a yellow oil (1.03 g) of methyl 4-(2-chlorophenyl)-5-ethoxycarbonyl-6-diethoxymethyl-1,4-dihydropyridine-3-carboxylate.

I.R. Spectrum (film) ν(cm⁻¹): 3350, 1700, 1590, 760.

N.M.R. Spectrum (δ, CDCl₃) ppm: 5.45 (1H, s), 6.20 (1H, s).

(21) Similarly, the following compounds were obtained:

(1) 2-(N-Benzyl-N-methylamino)ethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-diethoxymethyl-1,4-dihydropyridine-3-carboxylate.

I.R. Spectrum (film) ν (cm⁻¹): 3400, 1700, 1690, 1610, 1523, 1475, 1350, 1275, 1197, 1092, 1055, 755, 698.

N.M.R. Spectrum (δ: CDCl₃ + D₂ O) ppm: 1.21 (9H, t, J=7Hz), 2.21 (3H, s), 2.36 (3H, s), 2.63 (2H, t, J=6Hz), 3.5 (2H, s), 3.65 (2H, q, J=7Hz), 3.66 (2H, q, J=7Hz), 4.1 (2H, q), 4.18 (2H, t, J=6Hz), 5.18 (1H, s), 6.2 (1H, s), 6.86 (1H, s), 7.16 to 8.16 (4H, m).

(2) 2-(N,N-Diethylamino)ethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-diethoxymethyl-1,4-dihydropyridine-3-carboxylate (a brown oil).

(3) 2-Hydroxyethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-diethoxymethyl-1,4-dihydropyridine-3-carboxylate, m.p. 98° to 100° C.

(4) 2-hydroxyethyl 2-methyl-4-(2-nitrophenyl)-5-ethoxycarbonyl-6-diethoxymethyl-1,4-dihydropyridine-3-carboxylate.

I.R. Spectrum (film) ν (cm⁻¹): 3530, 3410, 3360 (shoulder), 1706 (shoulder), 1697, 1690 (shoulder), 1532, 1480, 1356, 1275, 1208, 1100, 1105, 860, 832, 785.

N.M.R. Spectrum (δ, CDCl₃) ppm: 1.0 to 1.45 (9H, m), 2.39 (3H, s), 2.2 to 2.73 (1H, broad), 3.4 to 4.5 (10H, m).

(5) Diethyl 2-methyl-4-(2-nitrophenyl)-6-ethylenedioxymethyl-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 152° to 153.5° C.

EXAMPLE 2

(1) To a solution of diethyl 2,6-bis(diethoxymethyl)-4-(2-chlorophenyl)-1,4-dihydropyridine-3,5-dicarboxylate (1.7 g) in acetone (17 ml) was added 6N-hydrochloric acid (1.5 ml) and stirred at room temperature for 3 hours. After removing the solvent, the residue was extracted with diethyl ether and the extract was washed with water and dried. The solvent was removed from the extract to give diethyl 2,6-diformyl-4-(2-chlorophenyl)-1,4-dihydropyridine-3,5-dicarboxylate (1.35 g). The product was recrystallized from diethyl ether to give pure yellowish granules, m.p. 85° to 86° C.

(2) To a solution of diethyl 2-methyl-4-(2-chlorophenyl)-6-diethoxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (452 mg) in acetone (5 ml) was added 6N-hydrochloric acid (0.2 to 0.3 ml) and stirred at room temperature for an hour. After removing acetone, the residue was extracted with ethyl acetate twice and the extract was washed with water and dried. The solvent was removed from the extract to give diethyl 2-methyl-4-(2-chlorophenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate. The product was recrystallized from a mixture of n-hexane and diethyl ether to give the pure product, m.p. 87° to 88° C.

(3) To a solution of dimethyl 2-methyl-4-(2-chlorophenyl)-6-(1-dimethoxyethyl)-1,4-dihydropyridine-3,5-dicarboxylate (409.9 mg) in acetone (5 ml) was added 6N hydrochloric acid (0.5 ml) and stirred at room temperature for 17 minutes. The reaction mixture was neutralized with an aqueous solution saturated with sodium bicarbonate and the solvent was distilled off under reduced pressure. Water was added to the residue and the mixture was allowed to stand to give crystals, which were collected by filtration and dried to give crystals (350.2 mg). These crystals were recrystallized from a mixture of n-hexane and ethyl acetate to give yellow granules of dimethyl 2-methyl-4-(2-chlorophenyl)-6-acetyl-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 161° to 162° C.

(4) To a solution of diethyl 2-methyl-4-(2-nitrophenyl)-6-diethoxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (1.1563 g) in acetone (10 ml) was added 6N-hydrochloric acid (2.5 ml) and stirred at room temperature for 30 minutes. After removing acetone, water was added to the residue and neutralized with aqueous solution of sodium bicarbonate. The precipitated solid was collected by filtration, washed with water and then dried to give yellowish powder of diethyl 2-methyl-4-(2-nitrophenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (0.9407 g). The product was recrystallized from a mixture of ethanol and n-hexane to give the pure product, m.p. 101° to 103° C.

(5) To a solution of diethyl 2-methyl-4-(3-nitrophenyl)-6-diethoxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (462.5 mg) in acetone (4 ml) was added 6N-hydrochloride acid (0.4 ml) and stirred at room temperature for an hour. After the reaction, the solvent was removed from the resultant solution. To the residue was added water, and the residue was pulverized. The powder was collected by filtration, washed with water and dried to give diethyl 2-methyl-4-(3-nitrophenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (360 mg), m.p. 130° to 133° C.

(6) To a solution of diethyl 2-methyl-4-(2-trifluoromethylphenyl)-6-diethoxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (5.2 g) in acetone (5 ml) was added 6N-hydrochloric acid (5 ml) and stirred at room temperature for about 1.5 hours. After removal of the acetone, water was added to the residue and the resultant aqueous solution was extracted with ethyl acetate twice. The extract was washed with water and dried and the solvent was removed therefrom to give a reddish oil (4.2 g) of diethyl 2-methyl-4-(2-trifluoromethylphenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate.

I.R. Spectrum (Nujol) ν (cm⁻¹): 3350, 1700, 1640, 1605, 1480, 1370, 1308, 1200, 1100, 1035, 950, 763.

N.M.R. Spectrum (δ: CDCl₃ + D₂ O) ppm: 1.2 (6H, t, J=7Hz), 2.4 (3H, s), 3.92 to 4.38 (4H, m), 5.72 (1H, s), 7.06 (1H, s), 7.24 to 7.62 (4H, m).

(7) To a solution of diethyl 2-methyl-4-(2-methoxyphenyl)-6-diethoxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (447.5 mg) in acetone (7.5 ml) was added 6N-hydrochloric acid (0.2 ml) and stirred at room temperature for an hour. The resultant mixture was treated in a similar manner to Example 2-4), to give reddish yellow crystals of diethyl 2-methyl-4-(2-methoxyphenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (373.2 mg). The product was recrystallized from a mixture of diethyl ether and n-hexane to give the pure product, m.p. 111° to 112° C.

(8) To a solution of diethyl 2-methyl-4-(2-chloro-5-nitrophenyl)-6-diethoxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (5.45 g) in acetone (54.5 ml) was added 6N hydrochloric acid (5 ml) and the resultant mixture was stirred at room temperature for 1.5 hours. After removal of the acetone from the reaction mixture, water was added to the residue and the mixture was allowed to stand for 15 minutes. The precipitated crystals were collected by filtration, washed with water and dried to give crystals (4.2 g). Thus obtained crystals (500 mg) were recrystallized from a mixture of n-hexane and ethyl acetate to give crystals (347 mg) of diethyl 2-methyl-4-(2-chloro-5-nitrophenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 172° to 173° C.

(9) To a solution of diethyl 2-methyl-4-(2-thienyl)-6-diethoxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (424 mg) in acetone (15 ml) was added 6N-hydrochloric acid (0.2 ml) and this solution was stirred at room temperature for an hour. The resultant solution was concentrated and the residue was extracted with diethyl ether. The extract was washed with water and dried and then the solvent was removed to give yellowish oil of diethyl 2-methyl-4-(2-thienyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate, which was soon crystallized. The product was recrystallized from a mixture of n-hexane and diethyl ether to give the pure product (247.7 mg), m.p. 67° to 68.5° C.

(10) To a solution of diethyl 2-methyl-4-(2-furyl)-6-diethoxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (6.6 g) in acetone (66 ml) was added 6N hydrochloric acid (6.6 ml) and the resultant mixture was stirred for one and three-fourths hour at room temperature. After removal of the acetone from the reaction mixture, the residue was extracted with ethyl acetate. The extract was washed with water, dried and concentrated. The resultant oil (6.1 g) was subjected to column chromatography on silica-gel with an eluent (a mixture of 20 parts of chloroform and one part of ethyl acetate by volume). The concentrate (oil, 2.4 g) of the fraction of the eluate which showed one spot on thin-layer chromatography gave crystals (1.79 g) and the concentrate (700 mg) of the fraction of the eluent which showed plural spots on thin-layer chromatography gave crystals (410 mg). These crystals were combined together and recrystallized from n-hexane to give needles (400 mg) of diethyl 2-methyl-4-(2-furyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 78° to 79.5° C.

(11) Starting from a mixture of 2-ethoxyethyl 2-methyl-4-(2-nitrophenyl)-5-ethoxycarbonyl-6-diethoxymethyl-1,4-dihydropyridine-3-carboxylate (1.9 g) in acetone (19 ml) and 6N hydrochloric acid (1.9 ml), was obtained, by applying an essentially similar manner to that of Example 2-(1), crystals of 2-ethoxyethyl 2-methyl-4-(2-nitrophenyl)-5-ethoxycarbonyl-6-formyl-1,4-dihydropyridine-3-carboxylate, m.p. 107° to 108° C. (recrystallized from diisopropyl ether).

(12) To a solution of 2-hydroxyethyl 2-methyl-4-(2-nitrophenyl)-5-ethoxycarbonyl-6-diethoxymethyl-1,4-dihydropyridine-3-carboxylate (2.5 g) in acetone (30 ml) was added 6N hydrochloric acid (1 ml) and treated in a substantially similar manner to those of Example 2(6) to give a viscous oil (2.10 g) of 2-hydroxyethyl 2-methyl-4-(2-nitrophenyl)-5-ethoxycarbonyl-6-formyl-1,4-dihydropyridine-3-carboxylate.

N.M.R. Spectrum (δ, CDCl₃) ppm: 6.07 (1H, s), 10.43 (1H, s)

(13) In a substantially similar manner to that of Example 2-6), was treated a mixture of benzyl 2-methyl-4-(2-nitrophenyl)-5-ethoxycarbonyl-6-diethoxymethyl-1,4-dihydropyridine-3-carboxylate (1.5 g) in acetone (15 ml) and 6N hydrochloric acid (1.5 ml) to give a reddish brown oil which was crystallized and washed with n-hexane to give crystals (1.30 g) of benzyl 2-methyl-4-(2-nitrophenyl)-5-ethoxycarbonyl-6-formyl-1,4-dihydropyridine-3-carboxylate.

I.R. Spectrum (Nujol) ν (cm⁻¹): 3400, 1699, 1673, 1608, 1530, 1490, 1380, 1355, 1220, 1110, 1030, 835, 795.

N.M.R. Spectrum (δ, CDCl₃) ppm: 1.21 (3H, t, J=7Hz), 2.38 (3H, s), 4 to 4.4 (2H, m), 5.07 (2H, s), 6.01 (1H, s),

6.9 (1H, broad s), 7.25 to 7.8 (9H, m), 10.33 (1H, s).

(14) Starting from a mixture of an oil (2.5 g) of 2-benzyloxyethyl 2-methyl-4-(2-nitrophenyl)-5-ethoxycarbonyl-6-diethoxymethyl-1,4-dihydropyridine-3-carboxylate in acetone (25 ml) and 6N hydrochloric acid (2 ml) was obtained a reddish oil (2.05 g) of 2-benxyloxyethyl 2-methyl-4-(2-nitrophenyl)-5-ethoxycarbonyl-6-formyl-1,4-dihydropyridine-3-carboxylate, in a substantially similar manner to that of FIG. 2-6).

I.R. Spectrum (film) ν (cm⁻¹): 3380, 1695, 1532, 1485, 1277, 1210, 1100, 1040, 860, 750.

N.M.R. Spectrum (δ, CDCl₃) ppm: 2.40 (3H, s), 4.48 (2H, s), 6.08 (1H, s), 10.40 (1H, s).

(15) Starting from a mixture of 2-phenoxyethyl 2-methyl-4-(2-nitrophenyl)-5-ethoxycarbonyl-6-diethoxymethyl-1,4-dihydropyridine-3-carboxylate (1.24 g) in acetone (12 ml) and 6N hydrochloric acid (1.2 ml) was obtained an oil (1.1 g) of 2-phenoxyethyl 2-methyl-4-(2-nitrophenyl)-5-ethoxycarbonyl-6-formyl-1,4-dihydropyridine-3-carboxylate, in a substantially similar manner to that of Example 2-6).

I.R. Spectrum (film) ν (cm⁻¹): 3400, 1700, 1640, 1600, 1530, 1480, 1350, 1240, 1200, 1100, 860, 785, 755, 692.

N.M.R. Spectrum (δ, CDCl₃) ppm: 1.2 (3H, t, J=7Hz), 2.4 (3H, s), 3.98 to 4.46 (6H, m), 6.03 (1H, s), 6.71 to 7.76 (9H, m), 10.4 (1H, s).

(16) To a solution of 2-ethoxyethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-diethoxymethyl-1,4-dihydropyridine-3-carboxylate (5.85 g) in acetone (60 ml) was added 6N hydrochloric acid (3 ml) and the resultant mixture was stirred at room temperature for about 2 hours. The solvent was distilled off under reduced pressure and water added to the residue. The mixture was extracted with ethyl acetate twice and the extract was washed with an aqueous sodium chloride solution and dried. The solvent was distilled off to give a reddish oil (5.7 g), which was turned into crystals. These crystals were pulverized with a mixture of n-hexane and diethyl ether and the resultant powder (4.81 g) was collected by filtration. The powder (1.81 g) was recrystallized from a mixture of diethyl ether and ethyl acetate to give orange-yellow granules (1.2 g) of 2-ethoxyethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-formyl-1,4-dihydropyridine-3-carboxylate, m.p. 100° to 101° C.

(17) To a solution of 2-(N-methyl-N-benzylamino)-ethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-diethoxymethyl-1,4-dihydropyridine-3-carboxylate (7.25 g) in acetone (70 ml) was added 6N-hydrochloric acid (7 ml) and the resultant mixture was stirred at room temperature for 3 hours. The solvent was distilled off under reduced pressure. Water was added to the residue, where an oily substance appeared. The aqueous mixture was adjusted to an alkaline medium by addition of power of sodium bicarbonate, and then extracted with ethyl acetate. The extract was washed with water and dried, and the solvent was distilled off under reduced pressure to give a reddish oil (5.8 g) of 2-(N-methyl-N-benzylamino)-ethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-formyl-1,4-dihydropyridine-3-carboxylate.

N.M.R. Spectrum (δ: CDCl₃ +D₂ O) ppm: 1.29 (3H, t, J=7Hz), 2.21 (3H, s) 2.45 (3H, s), 2.63 (2H, t, J=6Hz), 3.51 (2H, s), 3.95 to 4.42 (2H, t), 3.95 to 4.42 (2H, q), 5.28 (1H, s), 7.08 (1H, s), 7.28 to 8.12 (4H, m), 10.54 (1H, s).

I.R. Spectrum (Film) ν (cm⁻¹): 3350, 1735, 1700, 1690, 1635, 1600, 1525, 1480, 1350, 1279, 1215, 1100, 1030, 735.

(18) To a mixture of a brown oil (2.46 g) of 2-(N,N-diethylamino)ethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-diethoxymethyl-1,4-dihydropyridine-3-carboxylate in acetone (24.6 ml) was added 6N hydrochloric acid (2.46 ml) and this mixture was stirred for two hours at room temperature. The reaction mixture was adjusted to pH 7 with an aqueous solution of sodium bicarbonate and the acetone was distilled off. The residue was extracted with ethyl acetate, and the extract was washed with water, dried, and concentrated to give an oil (1.81 g) of 2-(N,N-diethylamino)ethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-formyl-1,4-dihydropyridine-3-carboxylate.

N.M.R. Spectrum (δ, CDCl₃) ppm: 2.03 (3H, s), 5.3 (1H, s), 10.47 (1H, s).

(19) To a mixture of diethyl 2-methyl-4-(3-hydroxyphenyl)-6-diethoxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (1.16 g) in acetone (10 ml) was added 6N hydrochloric acid (1 ml) and this mixture was stirred at room temperature for 1.5 hours. The solvent was distilled off under reduced pressure. The residue was added with water and pulverized. The resultant suspension was extracted with ethyl acetate and the extract was washed with water and dried over magnesium sulfate. The solvent was distilled off under reduced pressure and the residue was treated with diethyl ether to give crystals (0.8 g). The crystals (200 mg) was recrystallized from a mixture of n-hexane and diethyl ether to give pure crystals (130 mg) of diethyl 2-methyl-4-(3-hydroxyphenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 141.5° to 142.5° C.

(20) To a mixture of a yellow oil (360 mg) of methyl 4-(2-chlorophenyl)-5-ethoxycarbonyl-6-diethoxymethyl-1,4-dihydropyridine-3-carboxylate in acetone (10 ml) was added 6N hydrochloric acid (0.3 ml) and the resultant mixture was stirred for 1.5 hours at room temperaature, and the acetone was removed. Water was added to the residue and the mixture was extracted with ethyl acetate. The ethyl acetate layer was washed with water, dried and concentrated. The resultant orange oil (0.26 g) was crystallized and the crystals were washed with n-hexane to give yellowish-orange powder (80.7 mg) of methyl 4-(2-chlorophenyl)-5-ethoxycarbonyl-6-formyl-1,4-dihydropyridine-3-carboxylate.

I.R. Spectrum (Nujol) ν (cm⁻¹): 3300, 1690, 1675, 1491, 1442, 1376, 1303, 1221, 1186, 1090, 1060, 831, 757.

N.M.R. Spectrum (δ, CDCl₃) ppm: 1.0 (3H, t, J=7Hz), 3.68 (3H, s), 4.18 (2H, q, J=7Hz), 5.56 (1H, s), 7 to 7.6 (6H, m),

10.44 (1H, s).

EXAMPLE 3

(1) The solution of diethyl 2-methyl-4-(2-chlorophenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (377.8 mg), hydroxylamine hydrochloride (83.4 mg) and sodium carbonate (63.6 mg) in ethanol (1 ml) was stirred at room temperature for 30 minutes. After concentrating the resultant solution, to the residue was added water. After the mixture was extracted with ethyl acetate, the extract was washed with water, and dried. The dried extract was concentrated to give yellowish oil (476 mg). The oil was crystallized with n-hexane to give diethyl 2-methyl-4-(2-chlorophenyl)-6-hydroxyiminomethyl-1,4-dihydropyridine-3,5-dicarboxylate (318.8 mg), which was identified by converting to the corresponding 6-cyano compound, m.p. 136° to 137° C.

(2) A mixture of diethyl 2-methyl-4-(2-chlorophenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (756 mg) in ethanol (2 ml) and 85% hydrazine hydrate (141 mg) in water (1 ml) was stirred at room temperature for an hour. The ethanol was distilled off under reduced pressure and the residue was extracted with ethyl acetate. The extract was washed with water, dried over magnesium sulfate and concentrated under reduced pressure to give an oil (960 mg). The oil was subjected to a column chromatography on silica gel with an eluent a mixture of one part of benzene and one part of diethyl ether by volume! to give an oily substance (720 mg), which was allowed to stand for 14 days in a refrigerator to give needles (120 mg) of diethyl 2-methyl-4-(2-chlorophenyl)-6-hydrazonomethyl-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 107° to 110° C.

(3) To a mixture of diethyl 2-methyl-4-(2-chlorophenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (525.3 mg) and O-methylhydroxyamine hydrochloride (139.34 mg) in 99% ethanol (6 ml) was dropwise added a solution of sodium carbonate (88.5 mg) in water (1 ml) over the period of 20 minutes under stirring at room temperature. The mixture was stirred for another 10 minutes. The ethanol was distilled off under reduced pressure, and water was added to the residue. The aqueous mixture was extracted with diethyl ether and the extract was washed with water twice and a saturated aqueous solution of sodium chloride, dried and then concentrated under reduced pressure to give a yellow oil. The oil turned into crystals, and these crystals were washed with n-hexane to give yellow powder (504.6 mg). This powder was recrystallized from a mixture of 10 parts of n-hexane and one part of diethyl ether by volume to give yellow granules (301.5 mg) of diethyl 2-methyl-4-(2-chlorophenyl)-6-methoxyiminomethyl-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 110° to 112° C.

(4) A mixture of diethyl 2-methyl-4-(2-nitrophenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (1.1651 g), N,N-dimethyltrimethylenediamine (306.6 mg) and p-toluenesulfonic acid (catalytic amount) in dried benzene (20 ml) was refluxed under azeotropic dehydration for 4.5 hours. The resultant solution was washed with water and dried. The solvent was removed from the solution to give brown oil (1.4748 g) of diethyl 2-methyl-4-(2-nitrophenyl)-6- 3-(N,N-dimethylamino)propyl!iminomethyl-1,4-dihydropyridine-3,5-dicarboxylate.

I.R. Spectrum (Film) ν (cm⁻¹): 3350, 1710, 1695, 1534, 1487, 1280, 1200, 1100, 1043, 860, 828, 785, 753, 715, 680.

N.M.R. Spectrum (δ, CDCl₃) ppm: 1.18 (3H, t), 1.2 (3H, t), 2.25 (6H, s), 2.41 (3H, s), 3.67 (2H, broad t), 3.8 to 4.3 (8H, m), 5.97 (1H, s), 7.2 to 7.8 (4H, m), 7.8 (1H, broad s), 8.97 (1H, t, J=1Hz).

(5) A mixture of diethyl 2-methyl-4-(2-nitrophenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (970.9 mg), N,N-diethylethylenediamine (290.5 mg) and p-toluenesulfonic acid (catalytic amount) in dried benzene (20 ml) was refluxed under azeotropic dehydration for 4 hours. To the resultant solution was added diethyl ether and the solution was washed with water and dried. The solvent was removed to give red oil (1.1711 g) of diethyl 2-methyl-4-(2-nitrophenyl)-6- 2-(N,N-diethylamin)ethyl!iminomethyl-1,4-dihydropyridine-3,5-dicarboxylate.

I.R. Spectrum (Film) ν (cm⁻¹): 3350, 1700, 1685, 1528, 1475, 1351, 1273, 1090, 852, 821, 788, 746, 708.

N.M.R. Spectrum (δ, CDCl₃) ppm: 2.48 (3H, s), 5.99 (1H, s), 8.96 (1H, t, J=1Hz).

(6) A mixture of diethyl 2-methyl- 4-(2-nitrophenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (1.1651 g), 2-aminoethanol (185 mg) and p-toluenesulfonic acid (catalytic amount) in dried benzene (20 ml) was refluxed under azeotropic dehydration for 1.5 hours. After cooling to room temperature, water was added to the resultant solution. The mixture was washed twice with water. The aqueous layer was extracted with diethyl ether and the extract was combined with the benzene solution. The mixed solution was dried over magnesium sulfate and then the solvent was removed from the solution to give viscous oil (1.2397 g) of diethyl 2-methyl-4-(2-nitrophenyl)-6-(2-hydroxyethyl)iminomethyl-1,4-dihydropyridine-3,5-dicarboxylate.

I.R. Spectrum (Film) ν (cm⁻¹): 3500, 3360, 1694, 1536, 1484, 1280, 1220, 1101, 762, 753.

N.M.R. Spectrum (δ, CDCl₃) ppm: 1.13 (3H, t, J=7Hz), 1.20 (3H, t, J=7Hz), 2 (1H, broad s), 2.38 (3H, s), 3.8 to 4.3 (4H, m), 3.87 (4H, broad s), 5.96 (1H, s), 7.2 to 7.8 (4H, m), 7.8 (1H, broad s), 9.0 (1H, broad s).

(7)-(1) A mixture of diethyl 2-methyl-4-(2-trifluoromethylphenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (870 mg), sodium carbonate (112.1 mg) and hydroxylamine hydrochloride (147 mg) in ethanol (5 ml) was stirred at room temperature for 30 minutes. After removal of the ethanol, water and added to the residue and the solution was extracted with ethyl acetate. The extract was washed with a saturated aqueous solution of sodium chloride, dried over magnesium sulfate and concentrated under reduced pressure to give pasty oil (0.992 g). The oil was purified by column chromatography on silica gel with an eluent benzene (10) + ethyl acetate (1) ! to give yellow powder (0.52 g) of diethyl 2-methyl-4-(2-trifluoromethylphenyl)-6-hydroxyiminomethyl-1,4-dihydropyridine-3,5-dicarboxylate.

I.R. Spectrum (Nujol) ν (cm⁻¹): 3410, 1695, 1680, 1655, 1483, 1445, 1370, 1309, 1221, 1106, 1090, 1057, 1034, 1010, 985, 772.

N.M.R. Spectrum (δ: CDCl₃) ppm: 1.17 (3H, t, J=7Hz), 1.20 (3H, t, J=7Hz), 2.35 (3H, s), 3.8 to 4.4 (4H, m), 5.64(1H, broad s), 6.91 (1H, broad s), 7.2 to 7.7 (4H, m), 8.4 (1H, broad s), 8.8 (1H, s).

(7)-(2) To a solution of diethyl 2-methyl-4-(2-trifluoromethylphenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (1.23 g) and hydroxylamine hydrochloride (250.2 mg) in ethanol (5 ml) was added a solution of sodium carbonate (190.8 mg) in water (1.5 ml). The mixture was stirred at room temperature for 30 minutes and concentrated under reduced pressure. To the residue was added water and the mixture was extracted with ethyl acetate. The extract was washed with a saturated aqueous solution of sodium chloride, dried over magnesium sulfate and concentrated under reduced pressure to give an oil. The oil was crystallized with n-hexane to give crude crystals (1.09 g) of diethyl 2-methyl-4-(2-trifluoromethylphenyl)-6-hydroxyiminomethyl-1,4-dihydropyridine-3,5-dicarboxylate.

(8) To a mixture of 2-(N-methyl-N-benzylamino)-ethyl 2-methyl 4-(3-nitrophenyl)-5-ethoxycarbonyl-6-formyl-1,4-dihydropyridine-3-carboxylate (1.015 g) and hydroxylamine hydrochloride (116.8 mg) in ethanol (3 ml) was dropwise added slowly a solution of sodium carbonate (127.2 mg) in water (1 ml) and the resultant mixture was stirred at room temperature for 50 minutes. The ethanol was distilled off under reduced pressure and to the residue was added water and the mixture was extracted with ethyl acetate. The extract was washed with aqueous sodium chloride solution, dried and then concentrated under reduced pressure to give a yellow oil (1.01 g) of 2-(N-methyl-N-benzylamino)ethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-hydroxyiminomethyl-1,4-dihydropyridine-3-carboxylate.

I.R. Spectrum (film) ν (cm⁻¹): 3350, 1690, 1460, 1375, 1348, 1205, 1098, 1044, 738, 720, 700.

N.M.R. Spectrum (δ: CDCl₃) ppm: 1.22 (3H, t, J=7Hz), 2.26 (3H, s), 2.36 (3H, s), 2.70 (2H, t, J=6Hz), 3.58 (2H, s), 4.09 (2H, q, J=7Hz), 4.18 (2H, t, J=6Hz), 5.14 (1H, s), 7.1 to 8.1 (10H, m), 8.97 (1H, s)

According to a similar manner to those of the above Example 3-(1) to - (8), the following compounds were obtained:

(1) Diethyl 2-methyl-4-(2-nitrophenyl)-6-hydroxyiminomethyl-1,4-dihydropyridine-3,5-dicarboxylate.

(2) Diethyl 2-methyl-4-(2-chloro-5-nitrophenyl)-6-hydroxyiminomethyl-1,4-dihydropyridine-3,5-dicarboxylate.

(3) Diethyl 2-methyl-4-(2-furyl)-6-hydroxyiminomethyl-1,4-dihydropyridine-3,5-dicarboxylate.

(4) 2-ethoxyethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-hydroxyiminomethyl-1,4-dihydropyridine-3-carboxylate.

(5) 2-(N,N-Diethylamino)ethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-hydroxyiminomethyl-1,4-dihydropyridine-3-carboxylate.

Those compounds were prepared from the corresponding 6-formyl compounds in a similar manner to those of Examples 3-(1) to -(8) and were identified by converting them to the corresponding 6-cyano compounds

EXAMPLE 4

(1)-(1) A mixture of diethyl 2-methyl-4-(2-chlorophenyl)-6-hydroxyiminomethyl-1,4-dihydropyridine-3,5-dicarboxylate (0.6135 g) and N,N'-dicyclohexylcarbodiimide (804.6 mg) in pyridine (3 ml) was heated under reflux for 6 hours. The resultant solution was acidified with dilute hydrochloride acid and extracted with ethyl acetate. The insoluble product was filtered off and the filtrate was washed with water, dried over magnesium sulfate and evaporated under reduced pressure. To the residue was added diethyl ether and the mixture was filtered. The filtrate was concentrated under reduced pressure to give red oil (703.7 mg). The oil was purified by column chromatography on silica gel eluent : benzene (10) + ethyl acetate (1)! and crystallized with n-hexane. The crystals were recrystallized from a mixture of n-hexane and diethyl ether to give yellow crystals (417.1 mg) of diethyl 2-methyl-4-(2-chlorophenyl)-6-cyano-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 136° to 137° C.

(1)-(2) A mixture of diethyl 2-methyl-4-(2-chlorophenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (377.8 mg), sodium formate (125 mg) and hydroxylamine hydrochloride (79.93 mg) in formic acid (1.5 ml) was heated under reflux for an hour. Water was added to the reaction mixture and the mixture was extracted with ethyl acetate. The extract was filtered and the filtrate was washed with water, an aqueous sodium bcarbonate solution, water and a saturated aqueous solution of sodium chloride in turn and dried over magnesium sulfate. After the solvent was distilled from the solution, ether was added to the residue. The solution was filtered and the filtrate was concentrated under reduced pressure to give oil (210 mg). The oil was crystallized from a mixture of n-hexane and diethyl ether to give crystals (154.1 mg) of diethyl 2-methyl-4-(2-chlorophenyl)-6-cyano-1,4-dihydropyridine-3,5-dicarboxylate, which was identified with the authentic sample. The insoluble yellow powder (110 mg) which was collected by filtration in the above was the product of ethyl 1-oxo-6 -methyl-8-(2-chlorophenyl)-5,8-dihydro-1H-pyrido 2,3-d! 1,2!oxazine-7-carboxylate.

I.R. Spectrum (Nujol) ν (cm⁻¹): 3340, 3250, 1730, 1693, 1686 (shoulder), 1670, 1504, 1374, 1235, 1169, 1094, 972, 834, 778, 755,

N.M.R. Spectrum (δ:DMSO-D₆)

ppm : 0.98 (3H, t, J=7Hz), 2.37 (3H, s), 3.90 (2H, q, J=7Hz), 5.35 (1H, s), 7.1 to 7.5 (4H, m), 10.02 (1H, s), 10.35 (1H, s).

(1)-(3) A mixture of diethyl 2-methyl-4-(2-chlorophenyl)-6-formyl-1,4dihydropyridine-3,5-dicarboxylate (377.8 mg), sodium formate (125 mg), hydroxylamine hydrochloride (79.93 mg) in formic acid (1.5 ml) was stirred at room temperature for 5 minutes and acetic anhydride (0.2 ml) was added to the solution. The mixture was stirred at room temperature for 20 minutes and heated under reflux for an hour. After adding water to the resultant solution, the solution was extracted with ethyl acetate. The extract was washed with an aqueous sodium bicarbonate solution, water and a saturated aqueous sodium chloride solution in turn, dried over magnesium sulfate and concentrated under returned pressure to give brown oil (0.41 g). The oil was crystallized from a mixture of diethyl ether and n-hexane to give yellow powder (207 mg) of diethyl 2-methyl-4-(2-chlorophenyl)-6-cyano-1,4-dihydropyridine-3,5-dicarboxylate, which was identified with the authentic sample.

(1)-(4) A mixture of diethyl 2-methyl-4-(2-chlorophenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (377.8 mg), sodium acetate (164 mg) and hydroxylamine hydrochloride (80 mg) in acetic acid (1.5 ml) was stirred at room temperature for 30 minutes. After acetic anhydride (0.2 ml) was added to the solution, the solution was stirred at room temperature for an hour and then heated under reflux for an hour. Water was added to the reaction mixture, the solution was extracted with diethyl ether. The extract was washed with water, an aqueous sodium bicarbonate solution and water in turn and dried over magnesium sulfate. The solution was concentrated under reduced pressure to give yellow oil (410 mg). The oil was crystallized with n-hexane to give crystals (342.4 mg) of diethyl 2-methyl-4-(2-chlorophenyl)-6-cyano-1,4-dihydropyridine-3,5-dicarboxylate, which was identified with the authentic sample.

(2) A mixture of diethyl 2-methyl-4-(2-nitrophenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (2.03 g), hydroxylamine hydrochloride (417 mg). sodium acetate (861.4 mg) in acetic acid (15 ml) was stirred at room temperature for 30 minutes. Acetic anhydride (1 ml) was added to the reaction mixture, and the mixture was stirred at room temperature for 90 minutes and further refluxed for an hour. The acetic acid was distilled off under reduced pressure, and to the resultant residue was added water, and the aqueous mixture was adjusted to pH 7 to 8 with sodium bicarbonate and extracted with diethyl ether. The extract was washed with water, dried over magnesium sulfate and then concentrated under reduced pressure to give an oil. This oil was subjected to column chromatography on silica gel with an eluent a mixture of 4 parts of benzene and one part of ethyl acetate by volume!. The resultant oily substance (1.7 g) was crystallized by treating with a mixture of diethyl ether and n-hexane (1.5 g). These crystals were recrystallized from a mixture of diethyl ether and n-hexane to give pure crystals (1.23 g) of diethyl 2-methyl-4-(2-nitrophenyl)-6-cyano-1,4-dihydropyridine-3,5-dicarbonate, m.p. 126 to 127.5° C.

(3)-(1) A solution of the powder (0.49 g) of diethyl 2-methyl-4-(2-trifluoromethylphenyl)-6-hydroxyiminomethyl-1,4-dihydropyridine-3,5-dicarboxylate and thionyl chloride (1.5 ml) in dry diethyl ether (1.5 ml) was stirred at room temperature for 30 minutes. After the resultant solution was evaporated to dryness, water was added to the residue and the mixturewas extracted with ethyl acetate. The extract was washed with water, dried over magnesium sulfate and concentrated under reduced pressure to give a brown oil (0.39 g). The oil was purified by a column chromatography on silica gel with an eluent benzene (5) + ethyl acetate (1) ! and crystallized by treating with n-hexane to give yellow powder (50 mg). The powder was recrystallized from a mixture of diethyl ether and n-hexane to give crystals of diethyl 2-methyl-4-(2-trifluoromethyl-phenyl)6-cyano-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 140 to 143° C.

(3)-(2) A mixture of the crystals (1.09 g) of diethyl 2-methyl-4-(2-trifluoromethylphenyl)-6-hydroxyiminomethyl-1,4-dihydropyridine-3,5-dicarboxylate and N,N'-dicyclohexylcarbodiimide (1.319 g) in pyridine (5 ml) was heated under reflux for 6.5 hours. After removing pyridine, dilute hydrochloric acid was added to the residue and the mixture was stirred for 10 minutes. The mixture was extracted with ethyl acetate and the insoluble product was filtered off. The filtrate was washed with water, dried over magnesium sulfate and concentrated under reduced pressure to give brown oil (1.09 g). The oil was purified by column chromatography on silica gel with an eluent benzene (10) + ethyl acetate (1) ! to give oil 8720 mg). The oil was crystallized by treating with n-hexane and the precipitates were collected by filtration and washed with n-hexane to give yellow powder (610 mg). The power was recrystallized from a mixture of ether and n-hexane to give pure diethyl 2-methyl-4-(2-trifluoro-methylphenyl)-6-cyano-1,4-dihydropyridine-3,5-dicarboxylate, which was identified with the authentic sample, m.p. 140 to 143° C.

(3)-(3) A mixture of diethyl 2-methyl-4-(2-trifluoromethylphenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (205.7 mg), sodium acetate (82 mg) and hydroxylamine hydrochloride (40 mg) in acetic acid (1.5 ml) was stirred at room temperature for 30 minutes. After acetic anhydride (0.1 ml) was added, the solution was stirred at room temperature for 1.5 hours and then heated under reflux for an hour. To the resultant solution was added water and the solution was extracted with diethyl ether. The extract was washed with water, an aqueous sodium bicarbonte solution and water in turn, dried over magnesium sulfate and concentrated under reduced pressure to give oil (201 mg). The oil was purified by column chromatography on silica gel with an eluent benzene (5) +ethyl acetate (1) ! to give pure oil (172.4 mg). The oil was crystallized by treating with n-hexane to give powder (118 mg) of diethyl 2-methyl-4-(2-trifluoromethylphenyl)-6-cyano-1,4-dihydropyridine-3,5-dicarboxylate.

(4) A mixture of diethyl 2-methyl-4-(2-chloro-5-nitrophenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (3.70 g), hydroxylamine hydrochloride (695 mg). sodium acetate (1.436 g) in acetic acid (36 ml) was stirred at room temperature for 2.5 hours, and then acetic anhydride (2 ml) was added thereto. The resultant mixture was stirred for 30 minutes and refluxed for 1.5 hours. After removal of the acetic acid, water and ethyl acetate were added to the reaction mixture and the resultant mixture was washed twice with dilute sodium bicarbonate aqueous solution and then with an aqueous sodium chloride, and dried over magnesium sulfate. After removal of the solvent the residue was washed with diethyl ether to give powder (2.5 g). The powder was subjected to column chromatography on silica-gel with an eluent (a mixture of 10 parts of benzene and one part of ethyl acetate by volume). The fraction of the eluate which showed only one spot on thin-layer chromatography was concentrated to give crude crystals (450 mg) and the fraction of the eluate which showed plural spots on thin-layer chromatography was also concentrated to give crude crystals (1.0 g). Thus obtained cruse crystals were combined together and recrystallized from a mixture of benzene and ethyl acetate to give pure crystals (657 mg) of diethyl 2-methyl-4-(2-chloro-5-nitrophenyl)-6-cyano-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 204.5 to 205.5° C.

(5) A mixture of diethyl 2-methyl-4-(2-furyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylte (1.6 g), hydroxylamine hydrochloride (383.6 mg) and sodium acetate (787.6 mg) in acetic acid (14 ml) was stirred for 30 minutes at room temperature. To the mixture, acetic anhydride (1 ml) was added and stirred for 1.5 hours at room temperature and further stirred for an hour under reflux. After removal of the acetic acid from the reaction mixture, water was added to the residue and the mixture was extracted with ethyl acetate. The extract was washed with saturated sodium bicarbonate solution and water and dried, and then the solvent was distilled off under reduced pressure. The resultant brown oil (1.8 g) was purified by column chromatography on slica gel by an eluent (a mixture of 15 parts of chloroform and one part of ethyl acetate by volume). The concentrate (920 mg) of the fraction of the eluate which showed one spot on thin-layer chromatography and the concentrate of one (450 mg) which showed plural spots respectively gave crystals (totally 875 mg) and these were recrystallized from a mixture of diethyl ether and n-hexane to give pure crystals (818 mg) of diethyl 2-methyl-4-(2-furyl)-6-cyano-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 139 to 141° C.

(6)-(1) A mixture of 2-(N-benzyl-N-methylamino)ethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-hydroxyimino-methyl-1,4-dihydropyridine-3-carboxylate (0.91 g) and N,N'-dicyclohexylcarbodiimide (0.987 g) in pyridine (5 ml) was heated under reflux for 3 hours. After removal of the pyridine under reduced pressure, water was added to the residue. The mixture was extracted with ethyl acetate. The insoluble product was filtered off and the filtrate was washed with water, dried over magnesium sulfate and concentrated under reduced pressure to give red oil (1.6 g). The oil was purified by column chromatography on silica gel with an eluent benzene (2) + ethyl acetate (1)! to give a reddish oil (0.68 g) of 2-(N-benzyl-N-methylamino)ethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-cyano-1,4-dihydropyridine-3-carboxylate.

I.R. Spectrum (Nujol) ν (cu⁻¹) : 3320, 3250 (shoulder), 2240, 1708, 1685, 1525, 1500, 1345, 1293. 1210. 1100. 1030. 780. 735. 700. N.M.R. Spectrum (δ:CDCl₃) ppm : 1.25 (3H, t, J=7Hz), 2.15 (3H, s), 2.39 (3H, s), 2.62 (2H, t, J=7Hz), 3.48 (2H, s), 3.9 to 4.3 (4H, (CH₂ CH₃), t (COOCH₂ CH₂ N)), 5.26 (1H, s), 7.1 to 8.2 (10H, m).

The product obtained above was dissolved in diethyl ether. After adding ethanolic hydrochloric acid to the solution, the solution was evaporated to dryness. The residue was pulverized with n-hexane and the precipitating power was collected by filtration. The powder was recrystallized from an aqueous ethanol to give yellow pure crystals (460.8 mg) of the object compound hydrochloride, m.p. 228° to 229° C.

6-(2) A mixture of 2-(N-benzyl-N-methylamino)ethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-formyl-1,4-dihydropyridine-3-carboxylate (253.8 mg), sodium acetate (82 mg) and hydroxylamine hydrochloride (40 mg) in acetic acid (1 ml) was stirred at room temperature for 30 minutes. After acetic anhydride (0.1 ml) was added, the solution was stirred at room temperature for an hour and then heated under reflux for an hour. Water was added to the reaction mixture and the solution was neutralized with sodium bicarbonate and then extracted with ethyl acetate. The extract was washed with an aqueous sodium bicarbonate solution and water in turn, dried over magnesium sulfate and then concentrated under reduced pressure to give an oil (250 mg) (quantitatively) of 2-(N-benzyl-N-methylamino)-ethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-cyano-1,4-dihydropyridine- 3-carboxylate, which was identified with the authentic sample.

(7) Starting from a mixture of an oil (1.66 g) of 2-(N,N-diethylamino)ethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-formyl-1,4-dihydropyridine-3-carboxylate, hydroxylamine hydrochloride (0.302 g) and sodium acetate (0.593 g) in acetic acid (12 ml) and acetic anhydride (1.8 ml) was obtained crystals (700 mg) according to a similar manner to that of Example 4-2). These crystals were recrystallized from ethanol to give pure crystals (420 mg) of 2-(N,N-diethylamino)ethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-cyano-1,4-dihydropyridine-3-carboxylate, m.p. 150° to 152° C.

(8) A mixture of 2-ethoxyethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-formyl-1,4-dihydropyridine-3-carboxylate (3.00 g), hydroxylamine hydrochloride (0.5547 g), sodium acetate (1.1382 g) in acetic acid (10 ml) was stirred for 30 minutes at room temperature. To this mixture was added acetic anhydride (1.4 ml) and the resultant mixture was stirred for an hour at room temperature and refluxed for an hour. The acetic acid was distilled off under reduced pressure, and to the residue was added water. The resultant mixture was neutrallized with an aqueous solution of sodium bicarbonate and extracted with ethyl acetate twice. The extract was washed with water and an aqueous solution saturated with sodium chloride and dried. The solvent was distilled off and thus obtained viscous oily substance (3.19 g) was subjected to column chromatography on silica gel with an eluent a mixture of 5 parts of benzene and one part of ethyl acetate by volume!0 and a yellow oil (1.74 g) was obtained from the fraction which contained the designated product. The oil turned into crystals (1.56 g). These crystals were recrystallized from benzene to give yellow powder (1.5 g) of 2-ethoxyethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-cyano-1,4-dihydropyridine-3-carboxylate·1/3 benzene, m.p. 89° to 91° C. Thus obtained yellow powder was further recrystallized from a mixture of diethyl ether and n-hexane to give crystals of 2-ethoxyethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-cyano-1,4-dihydropyridine-3-carboxylate, m.p. 115° to 116° C.

(9) A mixture of diethyl 2-methyl-4-(3-nitrophenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (1.9418 g), hydroxylamine hydrochloride (399.6 mg), sodium acetate (820 mg) in acetic acid (7.5 ml) was stirred at room temperature for 30 minutes. After addition of acetic anhydride (1 ml), ther resultant mixture was stirred for an hour at room temperature and further refluxed for an hour. The acetic acid was distilled off, and water was added to the residue. The resultant aqueous mixture was neutralized by an aqueous solution saturated with sodium bicarbonate. A precipitating oil substance was extracted with ethyl acetate twice. The extract was washed with an aqueous solution of sodium chloride and dried. The solvent was distilled off under reduced pressure to give a orange-yellow oil (2.0103 g). This oil turned into crystals and these crystals were recrystallized from a mixture of diethyl ether, ethyl acetate and n-hexane to give yellow powder (0.9119 g). This powder was dissolved into a mixture of 5 parts of benzene and one part of ethyl acetate by volume and filtered on silica gel to give crystals (1.02 g). These crystals were recrystallized from a mixture of benzene and diethyl ether to give yellow granules (0.8479 g) of diethyl2-methyl-4-(3-nitrophenyl)-6-cyano-1,4 -dihydropyridine-3,5-dicarboxylate, m.p. 174° to 177° C.

(10) Starting from a mixture of a reddish oil (2.0 g) of 2-benzyloxyethyl 2-methyl-4-(2-nitrophenyl)-5-ethoxycarbonyl-6-formyl-1,4-dihydropyridine-3-carboxylate, hydroxylamine hydrochloride (336.9 mg), sodium acetate (662.9 mg) in acetic acid (15 ml) and acetic anhydride (1.5 ml) was obtained crystals (767 mg) according to a similar manner to that of Example 4-2). These crystals were recrystallized from a mixture of benzene and diethyl ether to give faint yellow crystals (450 mg) of 2-benzyloxyethyl 2-methyl-4-(2-nitrophenyl)-5-ethoxycarbonyl-6-cyano-1,4-dihydropyridine-3-carboxylate, m.p. 139° to 140° C. (further recrystallized from a mixture of diethyl ether and n-hexane).

(11) Starting from a mixture of 2 -phenoxyethyl 2-methyl-4-(2-nitrophenyl)-5-ethoxycarbonyl-6-formyl-1,4-dihydropyridine-3-carboxylate (1.03 g), hydroxylamine hydrochloride (178.6 mg) and sodium acetate (352 mg) in acetic acid (8 ml) and acetic anhydride (1 ml), there was obtained in a similar manner to that of Example 4-2) an oil (420 mg) of 2-phenoxyethyl 2-methyl-4-(2-nitrophenyl)-5-ethoxycarbonyl-6-cyano-1,4-dihydropyridine-3-carboxylate.

I.R. spectrum (KBr) ν (cm⁻¹) : 3330, 2250, 1710, 1600, 1530, 1500, 1300, 1216, 1110, 757.

N.M.R. Spectrum (δ, CDCl₃) ppm : 1.2 (3H, t, J=7Hz), 2.36 (3H, s), 4 to 4.4 (6H, m), 6.05 (1H, s), 6.73 (1H, m), 6.83 to 7.66 (9H, m).

(12) Starting from a mixture of 2-ethoxyethyl 2-methyl-4-(2-nitrophenyl)-5-ethoxycarbonyl-6-formyl-1,4-dihydropyridine-3-carboxylate (900 mg), hydroxylamine hydrochloride (167 mg) and sodium acetate (341 mg) in acetic acid (7 ml) and acetic anhydride (1 ml) was obtained by applying an essentially similar manner to that of Example 4-2), crystals (420 mg) of 2-ethoxyethyl 2-methyl-4-(2-nitrophenyl)-5-ethoxycarbonyl-6-cyano-1,4-dihydropyridine-3-carboxylate, m.p. 129° to 130.5° C. (recrystallized from a mixture of diethyl ether and n-hexane).

(13) Starting from a mixture of diethyl 2-methyl-4-(2-nitrophenyl)-6-formylmethyl-14-dihydropyridine-3,5-dicarboxylate, hydroxylamine hydrochloride and sodium acetate in acetic acid and acetic anhydride, was obtained an oil of diethyl 2-methyl-4-(2-nitrophenyl)-6-cyanomethyl-1,4-dihydropyridine-3,5-dicarboxylate, by applying an essentially similar manner to that of Example 4-2).

I.R. Spectrum (Liquid) ν (cm⁻¹) : 2210.

N.M.R. Spectrum (δ, CDCl₃) ppm : 1.17 (6H, t, J=7Hz), 2.32 (3H, s), 3.9 to 4.3 (4H, m), 4.78 (2H, s), 5.89 (1H, s), 7.14 (1H, broad s) 7.2 to 7.85 (4H, m),

EXAMPLE 5

(1) To a solution of diethyl 2,6-diformyl-4-(2-chlorophenyl)-1,4-dihydropyridine-3,5-dicarboxylate (272.7 mg) in 99% ethanol (7 ml) was added sodium borohydride (52.7 mg) under stirring at about 5° C. and the resultant mixture was further stirred at 5° C. for 10 minutes. The resultant solution was neutralized with dilute hydrochloric acid and ethanol was removed at room temperature under reduced pressure. To the residue was added water and the precipitates were collected by filtration, and then dried to give crude pale yellow crystals (261.0 mg) of diethyl 2,6-dihydroxymethyl-4-(2-chloro-phenyl)-1,4-dihydropyridine-3,5-dicarboxylate. The crude crystals were recrystallized from a mixture of ethanol and diethyl ether to give pure pale yellow needles, m.p. 190° to 191° C.

(2) To a solution of diethyl 2-methyl-4-(2-chlorophenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (1.5 g) in ethanol (30 ml) was added sodium borohydride (155 mg) under stirring and ths mixture was further stirred at room temperature for 2 hours. The resultant mixture was acidified with dilute hydrochloric acid and the solvent was removed. Water was added to the residue and the mixture was extracted twice with ethyl acetate. After the extract was washed with water and dried, the solvent was removed under reduced pressure from the extract to give a red oil (1.3525 g). The oil was dissolved in diethyl ether and allowed to stand at room temperature. After the insoluble product was removed by filtration, the filtrate was allowed to stand. The slowly precipitated crystals were collected by filtration and recrystallized from a mixture of diethyl ether and n-hexane to give pure crystals (92.0 mg) of diethyl 2-methyl-4-(2-chlorophenyl)-6-hydroxymethyl-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 143° C. The insoluble product obtained above was collected by filtration and recrystallized from ethyl acetate to give colorless prisms (241.5 mg) of ethyl 2-methyl-4-(2-chlorophenyl)-5-oxo-1,4,5,7-tetrahydrofuro- 3,4-b!pyridine-3-carboxylate, m.p. 211° to 212° C.

(3) To a mixture of dimethyl 2-methyl-4- 2-chlorophenyl!-6-acetyl-1,4-dihydropyridine-3,5-dicarboxylate (450 mg) in methanol (15 ml) was added gradually sodium borohydride (46.8 mg) under ice-cooling with stirring. The mixture was further stirred for 35 minutes under ice-cooling. The solution was neutralized with 2N-hydrochloric acid under ice-cooling and the solvent was distilled off under reduced pressure at a lower temperature than 30° C. on a water-bath. To the residue was added water and a small amount of an aqueous sodium bicarbonate to adjust the medium to pH 7 to 8. The resultant mixture was allowed to stand to give white powder, which was collected by filtration and dried to give powder (395.0 mg). To this powder was added diethyl ether (20 ml) and the mixture was stirred for about 30 minutes at room temperature. Insoluble white powder was collected by filtration and washed with diethyl ether. The filtrate and the washings were combined together and the solvent was distilled off at relatively low temperature to give crude crystals (100.5 g) of dimethyl 2-methyl-4-(2-chlorophenyl)-6-(1-hydroxyethyl)-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 145° to 147° C.

The insoluble white powder obtained above was collected by filtration and washed with diethyl ether to give crude white powder (264.2 mg) of methyl 2-methyl-4-(2-chlorophenyl)-5oxo-7-methyl -1,4,5,7-tetrahydrofuro 3,4-b!pyridine-3-carboxylate, m.p. 228° to 233° C.

(4) To a solution of diethyl 2-methyl-4-(2-nitrophenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (2.0881 g) in ethanol (20 ml) was gradually added sodium borohydride (0.1892 g) under stirring and the resultant mixture was further stirred at room temperature for an hour. The solution was acidified with dilute hydrochloric acid and stirred at room temperature for 30 minutes. After the resultant solution was filtered, the filtrate was concentrated under reduced pressure and extracted with ethyl acetate. The extract was washed with water and dried and then the solvent was removed to give orange oil (1.8596 g) of diethyl 2-methyl-4-(2-nitrophenyl)-6-hydroxymethyl-1,4-dihydropyridine-3,5-dicarboxylate. After the crude, product was dissolved in ethanol, the solution was filtered. The filtrate was concentrated under reduced pressure and the oily residue was allowed to stand for 3 days. Thus obtained crystals were recrystallized from ether to give pure product, m.p. 112° to 113° C.

The insoluble product obtained by filtration of the resultant solution in the above was recrystallized from ethanol to give pale yellow flakes (455.1 mg) of ethyl 2-methyl-4-(2-nitrophenyl)-5oxo-1,4,5,7-tetrahydrofuro- 3,4-b!pyridine-3-carboxylate, m.p. 220° to 222° C. The product was further recrystallized from ethyl acetate to give pure product, m.p. 221° to 223° C.

(5) To a suspended solution of diethyl 2-methyl-4-(3-nitrophenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (233 mg) in ethanol (10 ml) was added sodium borohydride (22.7 mg) at 0° to 5° C under stirring and this mixture was further stirred at about 5° C. for an hour and 10 minutes. After the reaction, the mixture was adjusted to pH 4 to 5 with 0.1N-hydrochloric acid, and then the solvent was removed under reduced pressure. The residue was extracted with ethyl acetate and the extract was washed with water and dried over magnesium sulfate. The extract was concentrated under reduced pressure and the residue was crystallized by treating with a mixture of diethyl ether and n-hexane. The precipitated crystals were collected by filtration, dried and recrystallized from a mixture of diethyl ether and n-hexane to give crystals of diethyl 2-methyl-4-(3-nitrophenyl)-6-hydroxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (152 mg), m.p. 141° to 142.5° C.

(6) To a solution of diethyl 2-methyl-4-(2-trifluoromethylphenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (1.0 g) in ethanol (20 ml) was gradually added sodium borohydride (92 mg) under stirring and ice-cooling and the resultant mixture was further stirred for 25 minutes. The resultant mixture was adjusted with 0.1 N hydrochloric acid to pH 4 to 5. The ethanol was removed under reduced pressure without heating so much, and water was added to the residue to give crystals. The crystals were collected by filtration to give crude crystals (1.2 g). These were recrystalized from a mixture of diethyl ether and n-hexane to give pure crystals of diethyl 2-methyl-4-(2-trifluoromethylphenyl)-6-hydroxymethyl-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 147° to 148.5° C.

(7) To a solution of diethyl 2-methyl-4-(2-methoxyphenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (1.1320 g) in ethanol (30 ml) was gradually added sodium borohydride (114 mg) under stirring and the resultant mixture was further stirred at room temperature for an hour. The resultant mixture was acidified with dilute hydrochloric acid. After removing ethanol from the mixture, water was added to the residue to solidify. The solid was collected by filtration, dried and washed with diethyl ether. The diethyl ether washings were concentrated to the volume of about 10 ml and stood at room temperature to give pale yellowish granules (372.5 mg) of diethyl 2-methyl-4-(2-methoxyphenyl)-6-hydroxymethyl-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 125° to 126° C. On the other hand, the solid obtained above, which was collected by filtration and washed with diethyl ether, was added to a mixed solution of p-toluenesulfonic acid (catalytic amount) in ethanol (5 ml) and the mixture was refluxed for one hour. After removal of ethanol, the residue was pulverized with diethyl ether and collected by filtration. The powder was recrystallized from a mixture of acetone and ethyl acetate to give colorless granules (114.8 mg) of ethyl 2-methyl-4-(2-methoxyphenyl)-5-oxo-1,4,5,7-tetrahydrofuro 3,4-b!-pyridine-3-carboxylate, m.p. 219° to 220° C.

(8) To a suspension of diethyl 2-methyl-4-(3-hydroxyphenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (600 mg) in ethanol (15 ml), was added sodium borohydride (63.5 mg) at 0° C. under stirring and the resultant mixture was further stirred for an hour. The resultant mixture was adjusted with 0.1N hydrochloric acid to pH 3 to 4 under ice-cooling. The ethanol was distilled off under reduced pressure and the residue was extracted with ethyl acetate. The extract was washed with water twice and an aqueous sodium chloride solution in turn, dried over magnesium sulfate and then concentrated under reduced pressure to give crystals (600 mg). These were recrystallized from a mixture of ethyl acetate and diethyl ether to give pure crystals (350 mg) of diethyl 2-methyl-4-(3-hydroxyphenyl)-6-hydroxymethyl-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 161.5° to 163° C.

(9) To a solution of diethyl 2-methyl-4-(2-thienyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (940.68 mg) in 99% ethanol (30 ml) was gradually added sodium borohydride (113.5 mg) under stirring and this was further stirred at room temperature for 2 hours. After removal of ethanol, the residue was extracted with ethyl acetate and the extract was washed twice with water and then dried. The solvent was removed from the extract to give a pale yellow oil. The oil was pulverized with n-hexane. The powder was dissolved in ethyl acetate. After collecting by filtration of the insoluble product, to the filtrate was added n-hexane and the mixture was allowed to stand in refrigerator. The appearing crystals were collected by filtration to give pale yellow granules (857.2 mg) of diethyl 2-methyl-4-(2-thienyl)-6-hydroxymethyl-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 125° to 126° C.

The insoluble product obtained above was collected by filtration to give powder (33.3 mg) of ethyl 2-methyl-4-(2-thienyl)-5-oxo-1,4,5,7-tetrahydrofuro 3,4-b!pyridine-3-carboxylate, m.p. 232° C.

(10) To a solution of 2-hydroxyethyl 2-methyl-4-(2-nitrophenyl)-5-ethoxycarbonyl-6-formyl-1,4-dihydropyridine-3-carboxylate (2.0 g) in ethanol (40 ml) was added bit-by-bit sodium borohydride (113.5 mg) at 5° C. under stirring. The mixture was further stirred at 5° C. for 30 minutes and acidified weakly with 50% acetic acid. After removal of the ethanol, to the residue was added water, and the mixture was made slightly alkaline with an aqueous solution of sodium bicarbonate, allowed to stand and then filtered, when it became clear. The precipitate (1.58 g) was collected by filtration and recrystallized from a mixture of ethanol and diisopropyl ether to give yellowish-orange granules (0.99 g) of 2-hydroxyethyl 2-methyl-4-(2-nitrophenyl)-5-ethoxycarbonyl-6-hydroxymethyl-1,4-dihydropyridine-3-carboxylate, m.p. 167° to 169° C.

(11) To a suspended solution of benzyl 2-methyl-4-(2-nitrophenyl)-5-ethoxycarbonyl-6-formyl-1,4-dihydropyridine-3-carboxylate (1.2 g) in ethanol (20 ml) was added sodium borohydride (60.6 mg) under ice-cooling and stirred, and further stirred for an hour at 0° C. and another an hour at 3° C. The reaction mixture was added with water and the resultant mixture was adjusted to pH 6 to 7 with 2N hydrochloric acid, and the solvent was distilled off. The residue was extracted with ethyl acetate and washed with water and dried. After removal of the solvent, the resultant oil (1.3 g) was purified by column chromatography on silica gel with an eluent (a mixture of ten parts of benzene and one part of ethyl acetate by volume) to give an oil which was immediately crystallized. The resultant crystals were recrystallized from a mixture of diethyl ether and n-hexane and dissolved in benzene. The benzene solution was subjected to azeotropic process five times to give pure crystals of benzyl 2-methyl-4-(2-nitrophenyl)-5-ethoxycarbonyl-6-hydroxymethyl-1,4-dihydropyridine-3-carboxylate, m.p. 51° to 57° C.

(12 ) To a suspension of 2-ethoxyethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-formyl-1,4-dihydropyridine-3-carboxylate (1.13 g) in ethanol (15 ml) was added sodium borohydride (80 mg) with stirring under ice-cooling, and this mixture was further stirred for an hour at the same temperature. The reaction mixture was adjusted with dilute hydrochloric acid to pH 6 under ice-cooling and then the solvent was distilled off. To the residue was added water and the aqueous mixture was extracted with diethyl ether. The extract was washed with water and dried over magnesium sulfate. Removal of the solvent gave an oil, which was crystallized by treating with n-hexane. These were crystallized from a mixture of diethyl ether and n-hexane to give pure crystals (900 mg) of 2-ethoxyethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-hydroxymethyl-1,4-dihydropyridine-3-carboxylate, m.p. 99° to 100° C.

(13) To a solution of 2-(N-methyl-N-benzylamino)ethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-formyl-1,4-dihydropyridine-3-carboxylate (1.5 g) in ethanol (15 ml) was added sodium borohydride (112 mg) under stirring and ice-cooling, and this mixture was further stirred for 20 minutes at the same temperature. The reaction mixture was adjusted with 0.1 N hydrochloric acid to pH 6 to 7 under ice-cooling, and concentrated under reduced pressure. To the residue was added ethyl acetate and water, and the aqueous layer was further washed with ethyl acetate twice. The extract obtained above and the washings were put together, washed with water, dried over magnesium sulfate, and concentrated under reduced pressure to give an oil (1.48 g) of 2-(N-methyl-N-benzylamino)ethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-hydroxymethyl-1,4-dihydropyridine-3-carboxylate.

I.R. Spectrum (film) ν (cm⁻¹) : 3390, 1730, 1680, 1650, 1600, 1520, 1460, 1345, 1200, 1100, 1025, 900, 780, 740, 700.

N.M.R. Spectrum (δ: CDCl₃ + D₂ O) ppm : 1.2 (3H, t, J=7Hz), 2.2 (3H, s), 2.38 (3H, s), 2.66 (2H, t, J=6Hz), 3.53 (2H, s) 3.97 to 4.26 (4H, m), 5.14 (1H, s), 7.28 to 8.15 (10H, m).

This obtained oil was dissolved int diethyl ether, and 21% ethanolic hydrochloric acid (225 mg) was added to the solution. A precipitating oil substance was washed with diethyl ether several times by decantation and pulverized to give powder (540 mg) of 2-(N-methyl-N-benzylamino)ethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-hydroxymethyl-1,4-dihydropyridine-3-carboxylate hydrochloride which began to decompose at 89° C. with turning to brown.

I. R. Spectrum (Nujol) ν (cm⁻¹) : 3300, 2600, 1680, 1525, 1375, 1350, 1200, 1095, 740, 700.

(14) To a mixture of powder (329 mg) of methyl 4-(2-chlorophenyl)-5-ethoxycarbonyl-6-formyl-1,4-dihydropyridine-3-carboxylate in ethanol (10 ml) was added sodium borohydride (25.11 mg) under ice-cooling. After further stirring for 50 minutes, the mixture was adjusted to pH 4 to 5 with dilute hydrochloric acid. After removal of the ethanol, water was added to the residue, which was extracted with ethyl acetate. The ethyl acetate layer was washed with water and dried and the residual crystals (about 280 mg) were dissolved in a mixture of diethyl ether and n-hexane and kept in a refrigerator to give pure crystals (184 mg) of methyl 4-(2-chlorophenyl)-5-ethoxycarbonyl-6-hydroxymethyl-1,4-dihydropyridine-3-carboxylate, m.p. 187 to 188° C.

(15) To a solution of diethyl 2-methyl-4-(2-nitrophenyl)-6- 2-(N,N-diethylamino)ethyl!iminomethyl-1,4 -dihydropyridine-3,5-dicarboxylate (1.1 g) in 99% ethanol (20 ml) was added sodium borohydride (115 mg) under stirring and the mixture was further stirred at room temperature for 5 hours. The resultant mixture was acidified with dilute hydrochloric acid. After removing ethanol, water was added to the residue and the mixture was washed with diethyl ether. The aqueous layer was basified with an aqueous solution of sodium bicarbonate and extracted with ethyl acetate. The extract was washed with water and dried. The solvent was removed from the extract to give greenish brown oil (0.8087 g) of a mixture including diethyl 2-methyl-4-(2-nitrophenyl)-6-!2-(N,N-diethylamino)-ethyl!aminomethyl-1,4-dihydropyridine-3,5-dicarboxylate (one part) and ethyl 2-methyl-4-(2-nitrophenyl)-5-oxo-6- 2-(N,N-diethylamino)ethyl!-1,4,5,7 -tetrahydropyrrolo 3,4 -b!pyridine-3-carboxylate (one part). After dissolving the mixture in ethanol, the solution was reluxed for 5 hours. The removal of the solvent gave crystals. These were recrystallized from ethanol to give yellow needles (729.9 mg) of ethyl 2-methyl-4-(2-nitrophenyl)-5-oxo-6- 2-(N,N-diethylamino)ethyl!-1,4,5,7-tetrahydropyrrolo 3,4-b!pyridine-3-carboxylate, m.p. 187° to 188° C.

(16) To a solution of diethyl 2-methyl-4-(2-nitrophenyl)-6-(2-hydroxyethyl)iminomethyl-1,4-dihydropyridine-3,5-dicarboxylate (1.2 g) in 95% ethanol (15 ml) was added sodium borohydride (115 mg) and stirred overnight at room temperature. The resultant mixture was wealky acidified with dilute hydrochloric acid and the ethanol was removed from the mixture. The residue was basified with an aqueous solution of sodium bicarbonate and then extracted with ethyl acetate. The extract was washed with water and dried over magnesium sulfate. The solvent was distilled off to give an oil of diethyl 2-methyl-4-(2-nitrophenyl)-6-(2-hydroxyethyl)-aminomethyl-1,4-dihydropyridine-3,5-dicarboxylate. This oil was dissolved in 95% ethanol (15 ml) and the solution was refluxed for 3 hours. Ethanol was removed from the solution to give a red oil. The oil was pulverized and recrystallized from a mixture of ethanol and diethyl ether to give an orange crystals (0.5998 g) of ethyl 2-methyl-4-(2-nitrophenyl)-5-oxo-6-(2-hydroxyethyl)-1,4,5,7-tetrahydropyrrolo- 3,4-b!pyridine-3-carboxylate. The product was further recrystallized from a mixture of ethanol and diethyl ether to give pure pale orange granules, m.p. 210° to 211° C.

EXAMPLE 6

(1) To a solution of diethyl 2-methyl-4-(2-chlorophenyl)-6-hydroxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (759.7 mg) in dried pyridine was dropwise added a solution of acetyl chloride (313.5 mg) in methylene chloride under cooling and stirring. The mixture was stirred overnight at room temperature. After removing the solvent, water was added to the residue, and the mixture was weakly acidified with dilute hydrochloric acid, and then extracted with diethyl ether. The extract was washed with an aqueous saturated sodium chloride solution and water in turn, and dried. The solvent was removed from the extract to give viscous oil (0.99 g). The oil was allowed to stand to pulverize and the crystals were washed with n-hexane and collected by filtration to give crude product (0.6931 g) of diethyl 2-methyl-4-(2-chlorophenyl)-6-acetoxymethyl-1,4-dihydropyridine-3,5-dicarboxylate. The crude product was recrystallized from a mixture of diethyl ether and n-hexane to give the pure product, m.p. 98° C.

(2) A mixed solution of diethyl 2-methyl-4-(2-chlorophenyl)-6-hydroxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (0.3798 g), pyridine (0.791 g) and succinic anhydride (0.1501 g) in dioxane (5 ml) was refluxed for 4.5 hours. The resultant solution was concentrated, acidified with dilute hydrochloric acid and extracted with diethyl ether. The extract was washed with dilute hydrochloric acid and water in turn. The diethyl ether extract was back-extracted with an aqueous saturated sodium bicarbonate solution and the aqueous solution was washed with diethyl ether. The aqueous solution was acidified with dilute hydrochloric acid to precipitate crystals. The crystals were collected by filtration, washed with water and then dried to give diethyl 2-methyl-4-(2-chlorophenyl)-6-(3-carboxypropionyl)oxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (419.3 mg), m.p. 130° to 131° C.

(3) To a solution of diethyl 2-methyl-4-(2-chlorophenyl)-6-hydroxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (0.7050 g) in pyridine (15 ml) was dropwise added a solution of ethyl 5-chloroformylpentanoate (0.7706 g) in methylene chloride under ice-cooling and the mixture was stirred at room temperature for 2.5 hours. After removing the pyridine water was added to residue and the mixture was extracted twice with ethyl acetate. The extract was washed with dilute hydrochloric acid, an aqueous sodium bicarbonate solution and water in turn, and then dried. The solvent was removed from the extract to give a yellow oil (1.0996 g). The oil was pulverized and recrystallized from a mixed solution of diethyl ether and n-hexane to give colorless flakes (0.7311 g) of diethyl 2-methyl-4-(2-chlorophenyl)-6-(5-ethoxycarbonylvaleryl)oxymethyl-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 91° to 92° C.

(4) To a mixture of sodium 3-(N-methyl-N-benzylamino)propionate (2.0 g) in diethyl ether (40 ml) was added thionyl chloride (10 ml) with stirring under ice-cooling. The resultant mixture was stirred at room temperature for 3 hours, heated under reflux for 2 hours and concentrated under reduced pressure to give a solid containing 3-(N-methyl-N-benzylamino)propionyl chloride. A suspension of thus obtained solid in methylene chloride (5 ml) was added to a solution of diethyl 2-methyl-4-(2-chlorophenyl)-6-hydroxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (0.76 g) in pyridine (5 ml) with stirring under ice-cooling. The mixture was stirred for an hour under ice-cooling and concentrated under reduced pressure, and water was added to the residue. The aqueous mixture was extracted with ethyl acetate and the extract was washed wth water, dried and concentrated under reduced pressure to give a brown oil (1.55 g). The oil was subjected to column chromatography on silica gel with an eluent a mixture of 2 parts of benzene and one part of ethyl acetate by volume! to give an oily substance. The oily substance was allowed to stand overnight to give crystals. These crystals were washed with n-hexane and recrystallized from a mixture of diethyl ether and n-hexane to give pure crystals of diethyl 2-methyl-4-(2-chlorophenyl)-6-(3-(N-methyl-N-benzylamino)-propionyloxy)methyl-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 86° to 87° C.

((5) To a mixture of diethyl 2-methyl-4-(2-nitrophenyl)-6-hydroxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (2.35 g) in pyridine (30 ml), was dropwise added a solution of acetyl chloride (942 mg) in methylene chloride (5 ml) under stirring and ice-cooling over the period of 7 minutes. The mixture was further stirred for 70 minutes at room temperature. The pyridine was distilled off under reduced pressure and ethyl acetate was added to the residue. The resultant mixture was washed twice with water adjusted to pH 4 with hydrochloric acid and then an aqueous solution of sodium chloride, dried and concentrated under reduced pressure to give an oily substance. This oily substance was crystallized by treating with a mixture of diethyl ether and a small amaunt of n-hexane, and collected crude crystals (2.5 g) were washed with n-hexane and thus obtained crystals were recrystallized from diethyl ether to give pure crystals (1.78 g) of diethyl 2-methyl-4-(2-nitrophenyl)-6-acetoxymethyl-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 89° to 90° C.

(6) To a solution of diethyl 2-methyl-4-(3-nitrophenyl)-6-hydroxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (1.95 g) in dried pyridine (25 ml) was dropwise added a solution of acetyl chloride (785 mg) in methylene chloride (5 ml) under ice-cooling and stirring over the period of 10 minutes. The mixture was further stirred for 50 minutes at room temperature. After removing the solvent, the residue was dissolved in ethyl acetate. The extract was washed with water five times and an aqueous solution of sodium chloride in turn, and dried over magnesium sulfate. The solvent was removed from the extract to give a red oil (2.47 g). The oil was crystallized by treating with diethyl ether, and the crystals were washed with n-hexane and collected by filtration to give crude crystals (2 g). These crystals were dissolved in diethyl ether and the mixture was filtered on silica gel. The filtrate was concentrated under reduced pressure and the crystalline residue was recrystallized from a mixture of diethyl ether and n-hexane to give pure crystals (1.45 g) of diethyl 2-methyl-4-(3-nitrophenyl)-6-acetoxymethyl-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 133° to 135° C.

(7) To a mixture of 2-(N-methyl-N-benzylamino)ethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-hydroxymethyl-1,4-dihydropyridine-3-carboxylate (630 mg) in pyridine (10 ml) was added a solution of acetyl chloride (146 mg) in methylene chloride (3 ml) under stirring and ice-cooling. The resultant mixture was further stirred at 50° to 60° C. for 2 hours. After removing the pyridine, water and ethyl acetate were added to the residue and the aqueous layer was adjusted to pH 4. The organic layer was separated, dried over magnesium sulfate and concentrated under reduced pressure to give an oily substance (800 mg). This oily substance was subjected to column chromatography on silica gel with an eluent a mixture of 2 parts of benzene and 1 part of ethyl acetate by volume! to give an oil (620 mg) of 2-(N-methyl-N-benzylamino)ethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-acetoxymethyl-1,4-dihydropyridine-3-carboxylate.

I.R. Spectrum (film)

ν (CM⁻¹): 3370, 1747, 1690, 1650, 1615, 1530, 1480, 1350, 1210, 1100, 1045, 740, 700.

N.M.R. Spectrum (δ: CDCl₃ +D₂ O) ppm: 1.18 (3H, t, J=7Hz), 2.18 (6H, s), 2.36 (3H, s), 2.6 (2H, t, J=6Hz), 3.5 (2H, s), 4.06 (2H, q, J=7Hz), 4.15 (2H, t, J=6Hz), 5.13 (1H, s), 5.31 (2H, s), 6.7 (1H, m), 7.23 to 8.08 (9H, m).

Thus obtained oil (580 mg) was dissolved in diethyl ether, and to the resultant solution was bit by bit added a diethyl ether solution of maleic acid to give precipitating oil. This oil was washed with diethyl ether twice by decantation and pulverized by n-hexane to give powder (405 mg) of 2-(N-methyl-N-benzylamino)ethyl-2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-acetoxymethyl-1,4-dihydropyridine-3-carboxylate maleate, m.p. 58° to 65° C.

(8) to a solution of diethyl 2-methyl-4-(2-nitrophenyl)-6-hydroxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (1.95 g) in pyridine (25 ml) was dropwise added a solution of benzoyl chloride (2.0 g) in methylene chloride (5 ml) over 5 minutes at 5° to 6° C. with stirring. The resultant mixture was stirred for 15 minutes at the same temperature and then at room temperature for 2 hours, and followed by stirring at 50° C. for an hour and a half. After the reaction was over, the pyridine was distilled off and to the residue was added ethyl acetate and water. The ethyl acetate layer was separated, washed with dil. hydrochloric acid twice and then aqueous solution of sodium bicarbonate, and dried over magnesium sulfate. The solvent was removed and the residue was soon crystallized by treating with diethyl ether and collected by filtration. These crude crystals were washed with a mixture of diethyl ether and a small amount of ethyl acetate to give crystals, which was recrystallized from ethyl acetate (25 ml) to give powders of diethyl 2-methyl-4-(2-nitrophenyl)-6-benzoyloxymethyl-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 156° to 157° C.

(9) To a solution of diethyl 2-methyl-4-(2-nitrophenyl)-6-hydroxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (1.95 g) in pyridine (25 ml) was dropwise added over 5 minutes a solution of p-chlorophenoxyacetyl chloride (3.07 g) in methylene chloride under stirring and ice-cooling. The resultant mixture was stirred at room temperature overnight under cooling with water at 20° C. After removal of the pyridine, water was added to the residue. The precipitated oily substance was extracted with ethyl acetate. The extract was adjusted to pH 4 to 5 with dil. hydrochloric acid, washed each three times with water and then an aqueous solution of sodium bicarbonate and dried over magnesium sulfate. The solvent was distilled off and the residual oil (4.75 g) was subjected to column chromatography on silica-gel using an eluent (benzene-ethyl acetate = 10:1 ) to give an oil (2.65 g) of diethyl 2-methyl-4-(2-nitrophenyl)-6-(4-chlorophenoxy)acetoxymethyl-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 86° to 88° C. (recrystallized from a mixture of diisopropylether and ethanol).

N.M.R. Spectrum (CDCl₃ + D₂ O) ppm: 1.13 (6H, t, J=7Hz), 2.2 (3H, s), 4.03, 4.08 (4H, q, J=7Hz), 4.73 (2H, s), 5.43 (2H, s), 5.88 (1H, s), 6.53 (1H, broad s), 6.76 to 7.83 (8H, m).

EXAMPLE 7

Stirring a solution of diethyl 2-methyl-4-(2-chlorophenyl)-6-hydroxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (1.1395 g) in dried pyridine (10 ml) at room temperature, a solution of p-toluenesulfonyl chloride (629.1 mg) in dried pyridine (10 ml) was dropwise added gradually thereto. The resultant mixture was stirred at room temperature for 1.5 hours and then heated at 80° C. for 4.5 hours with stirring. After removal of the pyridine, water was added to the residue and the resultant aqueous mixture was acidified with dil. hydrochloric acid and extracted twice with ethyl acetate. The extract was washed with dil. hydrochloric acid and then water, and dried. The resultant brown viscous oil was purified by column chromatography on silica-gel using an eluent (benzene:diethyl ether = 1:1 ) to give an orange oil, which was crystallized by treating with diethyl ether. The resultant crystals were collected by filtration and recrystallized from a mixture of diethyl ether and n-hexane to give orange-yellowish prisms (0.1926 g) of diethyl 2-methyl-4-(2 -chlorophenyl)-6-formyl-1,4-dihydropyridine- 3,5-dicarboxylate, m.p. 87° to 88° C., which was identified with an authentic sample.

EXAMPLE 8

(1) A solution of diethyl 2-methyl-4-(2-nitrophenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (0.9709 g) and hydrazine hydrate (0.1252 g) in n-propyl alcohol (10 ml) was stirred at room temperature for 30 minutes. The resultant mixture contained mainly diethyl 2-methyl-4 -(2-nitrophenyl)-6-hydrazonomethyl-1,4-dihydropyridine-3,5-dicarboxylate. Then the mixture was refluxed for 6 hours. After allowing to stand the resultant solution in a refrigerator overnight, the precipitating crystals were collected by filtration to give ethyl 2-methyl-4-(2-nitrophenyl)-5-oxo-1,4,5,6-tetrahydro-3-pyrido 2,3-d!-pyridazine-3-carboxylate (263.9 mg). The product was recrystallized from a mixture of ethanol and N,N-dimethylformamide to give the pure product, m.p. 279° to 281° C.

(2) A solution of diethyl 2-methyl-4-(2-chlorophenyl)-6-hydroxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (592.5 mg) and p-toluenesulfonic acid (catalytic amount) in ethanol (6 ml) was refluxed for 4 hours. After the resultant solution was concentrated, diethyl ether was added to the residue. The precipitating crystals were collected by filtration to give ethyl 2-methyl-4-(2-chlorophenyl)-5-oxo-1,4,5,7-tetrahydrofuro 3,4-b!pyridine-3-carboxylate (317.5 mg). The crude product was recrystallized from ethyl acetate to give colorless granules (210.3 mg), m.p. 211° to 212° C.

(3) A solution of diethyl 2-methyl-4-(2-thienyl)-6-hydroxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (400 mg) and p-toluenesulfonic acid (catalytic amount) in 99% ethanol (10 ml) was refluxed with stirring for 2 hours. After the resultant solution was concentrated, the residue was pulverized. The power was recrystallized from ethyl acetate to give colorless prisms (203.2 mg) of ethyl 2-methyl-4-(2-thienyl)-5-oxo-1,4,5,7-tetrahydrofuro 3,4-b!pyridine-3-carboxylate, m.p. 232° C.

EXAMPLE 9

(1) A mixture of diethyl 2-methyl-4-(2-chlorophenyl)-6-hydroxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (379.8 mg) and triphenylphosphine (314.7 mg) in carbon tetrachloride (5 ml) was refluxed for 3.5 hours. After the solvent was removed, the residue was dried under reduced pressure to give diethyl 2-methyl-4-(2-chlorophenyl)-6-chloromethyl-1,4-dihydropyridine-3,5-dicarboxylate. To this residue in 99% ethanol (10 ml) was added N-methylpiperazine (200 mg) and the solution was stirred at room temperature for 50 hours. Ethanol was removed from the reaction mixture and to the residue was added water. The mixture was extracted with ethyl acetate. After washing the extract with water, the extract was back-extracted with dilute hydrochloric acid. The aqueous layer was washed with diethyl ether, basified with an aqueous solution of sodium bicarbonate, and then extracted with ethyl acetate. The extract was washed with water, dried and then concentrated to give crude crystals (115.2 mg) of diethyl 2-methyl-4-(2-chlorophenyl)-6-(N-methylpiperazin-1-yl-methyl-1,4-dihydropyridine-3,5-dicarboxylate. The crude crystals were recrystallized from a mixture of ethanol and diethyl ether to give colorless needles, m.p. 179° to 180° C.

(2) A mixture of diethyl 2-methyl-4-(2-chlorophenyl)-6-hydroxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (1.1395 g) and triphenylphosphine (1.1803 g) in carbon tetrachloride (10 ml) was heated under reflux for 2 hours. After removing the solvent under reduced pressure, the residue was dissolved in 99% ethanol (20 ml). To the solution was added N-(2-hydroxyethyl)piperzine (859 mg) and the mixture was heated at 70° to 75° C. for 8 hours. The resultant mixture was concentrated under reduced pressure and the residue was dissolved in ethyl acetate. The solution was washed with water and then back-extracted with an aqueous dilute hydrochloric acid. The aqueous layer was washed with diethyl ether, alkalized with sodium bicarbonate and then extracted with ethyl acetate. The extract was washed with water, dried over magnesium sulfate and concentrated under reduced pressure to give crude crystals (560 mg). These were recrystallized from a mixture of ethanol and diethyl ether to give pure crystals (80 mg) of diethyl 2-methyl-4-(2-chlorophenyl)- 6- N-(2-hydroxyethyl)piperazin-1-yl!methyl-1,4-dihydropyridine-3,5 -dicarboxylate, m.p. 145° to 147° C.

(3) A mixture of 2-chloroethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxyycarbonyl-6-diethoxymethyl-1,4-dihydropyridine-3-carboxylate (8.5 g), N-methylbenzylamine (2.70 g) and triethylamine (2.6 g) in ethanol (40 ml) was heated under reflux for 56 hours. After removing the ethanol, the residue was dissolved in a mixture of ethyl acetate and water. The orgnic layer was separated and washed with water, dried over magnesium sulfate and concentrated under reduced pressure to give an oil (11 g). The oil was subjected to column chromatography on silica gel with an eluent a mixture of 10 parts of benzene and one part of diethyl ether by volume! to give an oil (7.35 g) of 2-(N-benzyl-N-methylamino)ethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-diethoxymethyl-1,4-dihydropyridine-3-carboxylate.

I.R. Spectrum (film) ν (cm⁻¹): 3400, 1700, 1690, 1610, 1523, 1475, 1350, 1275, 1197, 1092, 1055, 755, 698.

N.M.R. Spectrum (δ: CDCl₃ + D₂ O) ppm : 1.21 (9H, t, J=7Hz), 2.21 (3H, s), 2.36 (3H, s), 2.63 (2H, t, J=6 Hz), 3.5 (2H, s), 3.65 (2H, q, J=7Hz), 3.66 (2H, q, J=7Hz), 4.1 (2H, q), 4.18 (2H, t, J=6Hz), 5.18 (1H, s), 6.2 (1H, s), 6.86 (1H, s), 7.16 to 8.16 (4H, m).

(4) A mixture of 2-chloroethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-diethoxymethyl-1,4-dihydropyridine-2-carboxylate (2.0 g), diethylamine (1.75 g) and sodium iodide (60.3 mg) in n-propylalcohol (4 ml) was refluxed for 17 hours. After removal of the solvent from the reaction mixture, water and ethyl acetate were added to the residue. The ethyl acetate layer was washed twice with water, dried over magnesium sulfate, and concentrated to give a brown oil (2.46 g) of 2-(N,N-diethylamino)ethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-diethoxymethyl-1,4-dihydropyridine-3-carboxylate, which was identified by converting to the corresponding 6-formyl compound (oil) and then to the corresponding 6-cyano compound, m.p. 150 to 152° C.

(5) A mixture of 2-chloroethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-diethoxymethyl-1,4-dihydropyridine-3-carboxylate (1.491 g) and potassium carbonate (456.1 mg) in ethanol (30 ml) was refluxed for 6.5 hours. After removal of the ethanol, the residue was extracted with ethyl acetate. The ethyl acetate layer was washed twice with water and dried, and the solvent was distilled off to give a viscous oil (1.47 g). This oil was purified by column chromatography and the resultant oil (0.82 ) was crystallized and recrystallized from diisopropyl ether to give yellow granules (0.60 g) of 2-hydroxyethyl 2-methyl-4-(3-nitrophenyl)-5-ethoxycarbonyl-6-diethoxymethyl-1,4-dihydropyridine-3-carboxylate, m.p. 98° to 100° C.

A mixture of the above obtained yellow granules (1.46 g) obtained in Examples 1-12 and potassium carbonate (0.41 g) in 80% ethanol (20 ml) was refluxed for 6.5 hours. After removal of the ethanol, water was added to the residue, and the mixture was acidified with dilute hydrochloric acid and extracted with ethyl acetate. The extract was washed three times with water, dried, and concentrated to give a brown oil (1.54 g). Thus obtained oil was subjected to column chromatography on silica gel with an eluent (a mixture of five parts of benzene and two part of ethyl acetate by volume), and the fraction containing the designated substance was concentrated to give a reddish oil (1.31 g) of 2-hydroxyethyl 2-methyl-4-(2-nitrophenyl)-5-ethoxycarbonyl-6-diethoxymethyl-1, 4-dihydropyridine-3-carboxylate.

I.R. Spectrum (film) ν (cm⁻¹) : 3530, 3410, 3360 (shoulder), 1706 (shoulder), 1697, 1690 (shoulder), 1532, 1480, 1356, 1275, 1208, 1100, 1105, 860, 832, 785.

N.M.R. Spectrum (δ, CDCl₃) ppm : 1.0 to 1.45 (9H, m), 2.39 (3H, s), 2.2 to 2.73 (1H, broad), 3.4 to 4.5 (10H, m).

(6) A mixture of diethyl 2-methyl-4-(2-nitrophenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (388.37 mg), ethylene glycol (186.21mg) and p-toluenesulfonic acid (catalytic amount) in absolute benzene (5 ml) was refluxed for 45 minutes under azeotropic dehydration. The reaction mixture was allowed to stand and washed twice with an aqueous solution of sodium bicarbonate. After removal of the solvent, the residue immediately turned into crystals. Thus obtained crystals were recrystallized from a mixture of ethanol and diisopropyl ether to give yellow pure crystals (0.32 g) of diethyl 2-methyl-4-(2-nitrophenyl)-6-ethylenedioxymethyl-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 152 to 153.5° C. (7) A mixture of diethyl 2-methyl-4-(2-nitrophenyl)-6-hydroxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (1.9518 g) and triphenylphosphine (1.4425 g) in carbon tetrachloride (20 ml) was refluxed for 5 hours. After removal of the solvent, the residue was added to water and extracted with ethyl acetate. The extract was washed with water and dried. Removal of the solvent gave an orange-yellow oil (3.63 g). This oil was subjected to column chromatography on silica gel with an eluent (benzene : ethyl acetate = 5 : 2) to give an oil (517 mg) of diethyl 2-methyl-4-(2-nitrophenyl)-6-chloromethyl-1,4-dihydropyridine-3,5-dicarboxylate.

(8) To a solution of an oil (517 mg) of diethyl 2-methyl-4-(2-nitrophenyl)-6-chloromethyl-1,4-dihydropyridine-3,5-dicarboxylate in 95% ethanol (1 ml) was added sodium cyanide (93 mg), and the resultant mixture was stirred at room temperature for 2 hours. Addition of water to the reaction mixture precipitated an oil. The oil wax extracted twice with ethyl acetate, and the organic layer was washed with water twice and with a saturated solution of sodium chloride and dried. Removal of the solvent gave a foamy oil (0.42 g), which was subjected to column chromatography on silica gel with an eluent (benzene : ethyl acetate = 5:2) to give a reddish orange oil (0.2783 g) of diethyl 2-methyl-4-(2-nitrophenyl)-6-cyanomethyl-1,4-dihydropyridine-3,5-dicarboxylate.

I.R. Spectrum (liquid) ν (cm⁻¹) : 2210

EXAMPLE 10

(1) To a mixture of 2-allyloxybenzaldehyde (8.11 g) and ethyl 4,4-diethoxyacetoacetate (12.00 g) in benzene (about 31 ml) was added acetic acid (0.36 g) and to the resultant mixture was added each one third portion of piperidine (0.51 g) in benzene (about 4 ml) with an interval of 20 minutes. After refluxing for 2.5 hours the mixture was cooled to room temperature and benzene (50 ml) was added thereto. The resultant mixture was washed three times with water and dried over magnesium sulfate. Removing of the solvent, a red oil was gained and to this oil was added ethyl 3-aminocrotonate (8.56 g). The resultant mixture was warmed at 55 to 60° C. for 6.5 hours under stirring and further for 2 hours at 72° to 75° C. and finally for 2.5 hour at 105° to 107° C. The reaction mixture was subjected to column chromatograhy on silica gel with an eluent to give an oil (19.38 g) from the eluate. The oil (3.0 g) was further purified on silica gel column chromatography with an eluent (benzene : ethyl acetate = 20 : 1) to give an oil (1.77 g) of diethyl 2-methyl-4-(2-allyloxyphenyl)-6-diethoxymethyl-1,4-dihydropyridine-3,5-dicarboxylate

I.R. Spectrum (liquid) ν (cm⁻¹) : 3430, 1695, 1650, 1618, 1490, 1371, 1280, 1095, 930, 760

N.M.R. Spectrum (δ, CDCl₃) ppm : 1.0-1.5 (12H, m), 2.28 (3H, s), 3.4-4.3 (8H, m), 5.35 (1H, s), 6.17 (1H, s), ca 4.5, ca 5-5.6, ca 5.7-6.4 (5H, m), 6.5-7.4 (5H, m)

(2) To a solution of diethyl 2-methyl-4-(2-allyloxyphenyl)-6-diethoxymethyl-1,4-dihydropyridine-3,5-dicarboxylate (1.5 g) in acetone (15 ml) was added 6N-hydrochloric acid (15 ml) with stirring and the resultant mixture was further stirred for an hour and 45 minutes at room temperature. The solvent was removed, and addition of water to the residue resulted a yellowish suspension with precipitation of an oil, which was immediately solidified. After being allowed to stand for about 10 minutes, the precipitated solids were collected by filteration and washed with water and dried. Thus obtained crude crystals were recrystallized from a mixture of diisopropyl ether and acetone to give orange-yellow granules of diethyl 2-methyl-4-(2-allyloxyphenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 129° to 131° C.

(3) A mixture of diethyl 2-methyl-4-(2-allyloxyphenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (4.53 g), hydroxylamine hydrochloride (866.9 mg), sodium acetate (1.2093 g) in acetic acid was stirred at room temperature for an hour. Acetic anhydride (3.5 ml) was added to the mixture and the resultant mixture was stirred at 93° to 98° C. for 3 hours. The acetic acid was distilled off under reduced pressure, and the residue was neutralized with a saturated aqueous solution of sodium bicarbonate and extracted twice with methylene chloride. The extract was washed with water twice and dried. Removal of the solvent gave a brown oil (6.42 g), which was immediately crystallized. The crystals were pulverized with diisopropyl ether to give yellow powder (3.21 g), which was recrystallized from 90% methanol to give orange-yellow crystals of diethyl 2-methyl-4-(2-allyloxyphenyl)-6-cyano-1,4-dihydropyridine-3,5-dicarboxylate, m.p. 143° to 145° C.

(4) To a solution of diethyl 2-methyl-4-(2-allyloxyphenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (4.70 g) in ethanol (100 ml) was gradually added at 4° C. sodium borohydride (445.2 mg) and the resultant mixture was stirred at 4° C. for 1.5 hours under ice-cooling. The reaction mixture was acidified with 50% acetic acid and ethanol was removed. To the residue was added water and the aqueous mixture was stirred for 10 minutes. The powder was collected by filtration and washed with water to give crude crystals (4.49 g), which were recrystallized from methanol to give yellow crystals of diethyl 2-methyl-4-(2-allyloxyphenyl)-6-hydroxymethyl-1,4-dihydropiridine-3,5-dicarboxylate, m.p. 124° to 126° C. 

I claim:
 1. A compound of the formula: ##STR25## wherein R₁ is phenyl, nitrophenyl or halophenyl,R₂ and R₃ are each lower alkoxycarbonyl or N-lower alkyl-N-phenyl(lower)alkylamino(lower)alkoxycarbonyl, R₄ is lower alkanoyloxy(lower)alkyl, carboxyalkanoyloxy(lower)alkyl, lower alkoxycarbonyl(lower)alkanoyloxy(lower)alkyl, N-lower alkyl-N-phenyl(lower)alkylamino(lower)alkanoyloxy(lower)alkyl, chlorophenoxy(lower)alkanoyloxy(lower)alkyl and benzoyloxy(lower)alkyl, and R₅ is lower alkyl.
 2. A compound according to claim 1, whereinR₁ is nitrophenyl or halophenyl.
 3. A compound according to claim 2, whereinR₂ is lower alkoxycarbonyl, and R₃ is lower alkoxycarbonyl or N-(lower)alkyl-N-phenyl(lower)alkylamino(lower)alkoxycarbonyl.
 4. A compound according to claim 3, whereinR₄ is lower alkanoyloxy(lower)alkyl.
 5. A compound according to claim 4, wherein R₂ and R₃ are each lower alkoxycarbonyl.
 6. A compound according to claim 5, wherein R₁ is nitrophenyl.
 7. A compound according to claim 6, whereinR₁ is 2-nitrophenyl, R₂ and R₃ are each ethoxycarbonyl, R₄ is acetoxymethyl, and R₅ is methyl.
 8. A compound according to claim 6, whereinR₁ is 3-nitrophenyl, R₂ and R₃ are each ethoxycarbonyl, R₄ is acetoxymethyl, and R₅ is methyl.
 9. A compound according to claim 5, wherein R₁ is halophenyl.
 10. A compound according to claim 9, whereinR₁ is 2-chlorophenyl, R₂ and R₃ are each ethoxycarbonyl, R₄ is acetoxymethyl, and R₅ is methyl.
 11. A compound according to claim 3, wherein R₄ is carboxy(lower)alkanoyloxy(lower)alkyl.
 12. A compound according to claim 11, whereinR₁ are each halophenyl, R₂ and R₃ is lower alkoxycarbonyl.
 13. A compound according to claim 12, whereinR₁ is 2-chlorophenyl, R₂ and R₃ are each ethoxycarbonyl, R₄ is 3-carboxypropionyloxymethyl, and R₅ is methyl.
 14. A compound according to claim 3, wherein R₄ is lower alkoxycarbonyl(lower)alkanoyloxy(lower)alkyl.
 15. A compound according to claim 14, wherein R₁ is halophenyl, and R₂ and R₃ are each lower alkoxycarbonyl.
 16. A compound according to claim 15, whereinR₁ is 2-chlorophenyl, R₂ and R₃ are each ethoxycarbonyl, R₄ is 5-(ethoxycarbonyl)valeryloxymethyl, and R₅ is methyl.
 17. A compound according to claim 4, whereinR₂ is lower alkoxycarbonyl, and R₃ is N-lower alkyl-N-phenyl(lower)alkylamino(lower)alkoxycarbonyl.
 18. A compound according to claim 3, wherein R₄ is N-(lower)-alkyl-N-phenyl(lower)alkylamino(lower)alkanoyloxy(lower)-alkyl.
 19. A compound according to claim 18, wherein R₁ is halophenyl, and R₂ and R₃ are each lower alkoxycarbonyl.
 20. A compound according to claim 19, whereinR₁ is 2-chlorophenyl, R₂ and R₃ are each ethoxycarbonyl, R₄ is 3-(N-benzyl-N-methylamino)propionyloxymethyl, and R₅ is methyl.
 21. A compound according to claim 3, wherein R₄ is benzoyloxy(lower)alkyl.
 22. A compound according to claim 21, wherein R₁ is nitrophenyl, and R₂ and R₃ are each lower alkoxycarbonyl.
 23. A compound according to claim 22, whereinR₁ is 2-nitrophenyl, R₂ and R₃ are each ethoxycarbonyl, R₄ is benzoylmethyl, and R₅ is methyl.
 24. A compound according to claim 3, wherein R₄ is chlorophenoxy(lower)alkanoyloxy(lower)alkyl.
 25. A compound according to claim 24, wherein R₁ is nitrophenyl, and R₂ and R₃ are each lower alkoxycarbonyl.
 26. A compound according to claim 25, whereinR₁ is 2-nitrophenyl, R₂ and R₃ are each ethoxycarbonyl, R₄ is 2-(4-chlorophenoxy)acetoxymethyl, and R₅ is methyl.
 27. A compound according to claim 17, wherein R₁ is nitrophenyl.
 28. A compound according to claim 27, whereinR₁ is 3-nitrophenyl, R₂ is ethoxycarbonyl, R₃ is 2-(N-methyl-N-benzylamino)ethoxycarbonyl, R₄ is acetoxymethyl, and R₅ is methyl.
 29. A method for effecting vasodilation in humans and mammals which comprises administering thereto an effective amount of the compound of claim
 1. 30. A method for effecting vasodilation in humans and mammals which comprises administering thereto an oral daily dose of 0.1 to 500 mg. or 10 to 25% thereof intravenously of the compound of claim
 1. 31. A method for effecting vasodilation in humans and mammals which comprises administering thereto an oral daily dose of 1 to 50 mg. or 10 to 25% thereof intravenously of the compound of claim
 1. 32. A method for effecting vasodilation in humans and mammals which comprises administering thereto an oral daily dose of 1 μg to 10 mg./kg. or 10 to 25% thereof intravenously of the compound of claim
 1. 33. A method for effecting vasodilation in humans and mammals which comprises administering thereto an oral daily dose of 0.5 to 5 mg./kg. or 10 to 25% thereof intravenously of the compound of claim
 1. 